This is despite Bank of England base rates running at historically low levels.
During the past six years, ISA savers have consistently put more than two thirds of their money in cash within ISAs, instead of stocks and shares.
The latest HMRC figures show the split 73% in cash and 27% in stocks and shares.
Confirming that cash is still king for ISA savers comes around the same time Citizens Advice revealed retirees also have a preference for cash.
They reported recently that three in ten retirees who are making use of pension freedoms are placing the money withdrawn from their pension pots in a bank account.
Looking over the ISA data from HMRC, it shows that a preference for cash is strongest amongst low earners, women and the young.
Those earning less than £30,000 are reported to place 83% of their ISA money in cash.
This is compared to those earning over £100,000 who place just 32% of their money in cash.
Women place 80% of their ISA money in cash, compared to men who place 72%.
Those aged under 35 place 92% of their ISA money in cash, compared to those aged 55+ placing just 72%.
Commenting on the data, Alistair McQueen, Savings and Retirement Manager at Aviva, said:
“ISA savers appear to disregard the old adage that ‘you have to speculate to accumulate’.
“While the Bank of England base rate has hit a historic low, ISA savers continue to demonstrate a love of low-risk cash. They have continued to place more than two-thirds of their money in cash.
“This is particularly the case amongst low earners, women and the young.
“At times of economic uncertainty, an aversion to risk may be understandable, but could savers be losing out?
“We will watch with interest to see how saving habits develop as the health of the economy and the level of the base rate evolves.”