Stac Lee rises to 172m (564ft) above the North Atlantic and Stac an Armin to 196m (643ft).
St Kildans harvested gannets and great auks from the cliffs of Stac an Armin. St Kilda's last 36 residents left the islands in the 1930s.
At the weekend, Assynt Mountain Rescue Team members Bob Kerr, of Portskerra, and Tim Hamlet, of Achiltibuie, climbed to the summits of both sea stacks.
The pair, who were among 12 climbers working together, managed to make their climbs during a spell of fine autumn weather.
Mr Kerr said the dry conditions made negotiating droppings left by thousands of seabirds on Stac Lee a little easier.
He said: "The ascent up and along the exposed ledges and the summit slope involved stepping on and moving up through abandoned gannet nests.
"Thankfully there had been a period of relatively dry warm weather in the days before this trip and this resulted in the guano in the nesting areas being fairly dry and stable.
"We would not enjoy ascending these slopes if the guano had been wet as it would have been excessively slippery."
Once on the top of Stac an Armin, the two climbers were able to take in clear views of St Kilda and the Western Isles.
Mr Kerr said: "The views across the entire St Kilda archipelago were awe inspiring as Boreary, Stac Lee, Stac Levenish, An Dun, Hirta and Soay could all be seen from the one spot.
"The hills of Harris were also visible on the far horizon."

Output rose 9.3% from a year ago, which was up from March's figure of 8.9% but below market forecasts for a 9.5% rise.
Fixed-asset investment also weakened in the first four months of 2013.
Last week, a separate survey suggested that manufacturing activity, a subset of industrial production, grew at a slower pace in April.
"This is not the start of a rally, it is a sputtering whimper as momentum continues to fade," said economists at IHS Global Insight.
By Linda YuehChief business correspondent
IHS also said that slowing fixed-asset investment - a key measure of government spending - suggested weakness in manufacturing and infrastructure construction, and warned that the pace could fall further amid government efforts to curb the housing market.
Separately, Bank of America Merrill Lynch analysts also warned that there was an increased "downside risk" to the economy.
China's economy expanded at an annual rate of 7.7% in the first three months of the year, down from 7.9% in the previous quarter.
Officials have warned that the economy is set to slow as the government attempts to rebalance the economy by getting domestic consumer demand to drive growth, rather than investments and exports.
This attempt now appears to be having an impact. According to government statistics, in the first three months of this year, the largest part of the economy was services - not manufacturing.

The builder said it would construct 139 homes at Duddingston Park South, Duddingston, and 165 at Newcraighall Village.
Barratt Homes will also build a total of 102 affordable homes between the two developments.
Newcraighall Village and Duddingston Park South are both set to launch later this year.
Anne Ross, sales director at Barratt Homes for the East of Scotland, said: "2014 has been buoyant year for new homes sales and we are pleased to be launching these two new developments in the Edinburgh area, to allow us to keep up with demand.
"With a wide selection of modern homes on offer and in sought-after locations, we hope these developments will be extremely popular."
The remote archipelago of St Kilda is home to the UK's highest sea stacks.
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Industrial production in China recorded a smaller-than-expected rise in April, underlining worries that the economy may be losing steam.
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Barratt Homes has confirmed it is pressing ahead with plans to build 400 new homes in the east of Scotland.