Dasilva, 19, is yet to play for Chelsea but impressed in 10 appearances for the Addicks at the end of last season.
The full-back captained England Under-19s to their first win at the European Championship this summer, as the Young Lions beat Portugal 2-1 in the final.
"He brings pace, talent, desire and a willingness to improve," Charlton boss Karl Robinson told the club website.
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The 22-year-old striker was one of three AC Milan players targeted during their match against Roma on Sunday, which was halted for two minutes.
"If it happens one more time, I'm going to leave the pitch, because it's so stupid," the Italy international said.
"I was about to leave, but they will think I wanted to leave because we had difficulty with the game."
AC Milan were down to 10 men at the time when the Serie A fixture at their San Siro stadium was temporarily stopped. The game only restarted after the visiting Roma supporters were ordered to cease their behaviour.
Roma, who were fined 50,000 euros (£42,400) by the Italian Football League for the incident, released a statement on Monday condemning the actions of their supporters and promised to "face this issue head-on".
The punishment was criticised by Fifa president Sepp Blatter, who told the world governing body's website: "They have not made any investigation of what happened. Just to give a pecuniary sanction is not valid, not acceptable."
Balotelli, who has scored 11 goals in 12 games since his January switch from Manchester City, said the incident had altered his thinking about the best way to tackle the problem.
He told CNN: "I always said if it happens in the stadium, I would just behave as if nobody had done anything and that I don't care, but now I think I've changed my mind a bit."
There have been a number of incidents this season involving racial abuse of AC Milan's players.
A January friendly between Milan and Pro Patria was suspended because of racist chants aimed at Kevin-Prince Boateng.
The following month, Inter Milan were fined 50,000 euros after their fans were found to have abused their former player Balotelli in the Milan derby.
And in April, champions Juventus were fined 30,000 euros (£25,000) after their supporters racially abused the AC Milan players.

21 October 2016 Last updated at 15:03 BST
In 2008, about 40 were recorded on the seahorse study site at South Beach in the bay, but none have been spotted there since 2013.
Miranda Krestovnikoff has been investigating for Inside Out and speaking to Neil Garrick-Maidment, from the Seahorse Trust, and the Royal Yachting Association's Emma Barton.

The move is just one of several waste and recycling options considered by the council on Thursday.
Black bags are currently collected fortnightly.
The council's head of environment, Richard Brown said there will be "high public interest" whatever they come up with.
A report before the policy scrutiny committee outlined the challenges faced by the council's waste service as a result of funding pressures.
It said Â£1.2m needed to be saved over the next four years. This is in addition to potential fines for missing statutory performance targets.
Five options were presented to the committee. They looked at what was being collected, how often and by what means.
Options for black bin bag collection were weekly, fortnightly and three-weekly, while limiting the number of customer-provided sacks to two or three.
Pembrokeshire council  stopped supplying residents with free black bags in 2016.
The report also outlined an opportunity to save money by working with Ceredigion council, which faces "many of the same challenges".
The committee's comments will be reported to Pembrokeshire council's cabinet before a decision is made.
Mr Brown said waste services "was the one service we all have a vested interest in" and that they have to "do the best they can" and "look at future change".
Jay Dasilva has signed a new four-year deal with Chelsea and rejoined Charlton Athletic on a season-long loan.
[NEXT_CONCEPT]
Mario Balotelli has threatened to walk off the pitch if he is ever again subjected to racist abuse from fans.
[NEXT_CONCEPT]
Spiny seahorses may soon be locally extinct at Studland Bay in Dorset, according to the Seahorse Trust.
[NEXT_CONCEPT]
Black bin bags could be collected every three weeks in Pembrokeshire as the council looks to meet "severe budget cuts" and performance targets.