Historic Scotland reported 1,692,611 visitors at its attractions between June and August this year, an increase of 14.8% on the same period last year.
The agency operates 78 ticketed venues across the country, making it Scotland's biggest operator of visitor attractions.
Its flagship attraction Edinburgh Castle saw visitor numbers increase by 26% during the three-month summer period compared with last year.
August alone saw 229,940 visitors go through the doors of the castle, an increase of 35.8%, more than any single month ever recorded.
Linlithgow Palace, the birthplace of Mary, Queen of Scots, welcomed in excess of 37,548 visitors, up 36%, and St. Andrews Castle was up 9.3%.
Iona Abbey, on the Isle of Iona, also saw a surge in visitors over the summer - up 13.5% to 34,957.
Culture Secretary Fiona Hyslop said: "These figures illustrate the important role that heritage plays for modern day Scotland.
"The benefits are many, in terms of highlighting our diverse culture both at home and abroad, but also in terms of supporting and driving economic growth.
"All of the income generated is invested back into our rich historic environment. Most recently this has included a significant investment in Iona Abbey to continue to provide world-class attractions for Scots and overseas visitors alike.
"As the custodians of Scotland's rich heritage, it is important that we continue to engage with both Scots and visitors from around the world as we look forward to Scotland welcoming the world in 2014."
Historic Scotland data showed increases in visitors from the emerging tourism markets of China and Russia while Scots themselves contributed to a rise in visitor numbers to attractions outwith Edinburgh, Stirling and Urquhart castles.
Membership also continued to attract domestic visitors, at an all-time high, up 7% on the same period last year.
Stephen Duncan, director of commercial and tourism for Historic Scotland, said 2012 saw a "flattening out of visitors".
"We had always expected 2013 to see a return to previous levels but the summer performance has surpassed all expectations," he said.
"It's particularly encouraging to see patterns at Edinburgh (Castle), Scotland's number one paid-for tourism attraction, replicated at many of our other properties across our estate who enjoyed record-breaking summers and substantial increases in visitors.
"As an organisation we are continuing to evolve our offering to visitors - be that through our retail, e-commerce and membership products, or investing in areas such as our award winning events programme to make history an accessible, fun and enjoyable part of people's lives."