Research among almost 300 directors in 100 FTSE companies found the average pension pot increased by £41,000 to £4.7 million.
The TUC said bosses continued to enjoy "platinum-plated" pensions, with most still able to retire at 60.
More directors are moving to defined contribution pensions, enjoying a "sharp increase" in employer contributions, said the report.
The union organisation said top bosses were finding new ways of rewarding themselves. TUC general secretary Frances O'Grady said: "Britain's top bosses already enjoy a level of pay and bonuses beyond common decency."