Aviva says that, only 39% of people surveyed could confidently estimate the value of their pension pot.
There is now record membership of occupational defined contribution pensions, at 23.4million - up from 21.7million last year.
Other fresh data reveals that individuals in the UK hold a record £15.2trillion of private wealth - and pensions represent the largest proportion of this figure at £6.4trillion.
This exceeds £5.5trillion in property and the £3.3trillion in other assets, including around £2trillion in cash. Aviva states that auto-enrolment has been the biggest driver of participation into pension saving over the last decade.
When it was introduced in 2012, only 39% of private-sector workers were actively saving for their retirement.
This figure is now more than 70%.
But Aviva adds:
"It is risky to assume that this participation rate has driven clearer understanding.
"Despite a significant increase in participation rates, the proportion of adults who agree they 'understand enough about pensions' has only increased by 1% in the last 10 years from 43% to 44%."
More than half of those surveyed could estimate the value of their property quite accurately.
This figure rises to 61% of those who are retired.
However, despite pensions potentially being their biggest asset, only 39% of people could confidently estimate the value of their pension pot.
One in 10 people surveyed were "very unconfident" about estimating the current value of their pension savings.
The need to close the gap between pension participation and understanding is now critical, says Aviva.
Over the next century, it is estimated that the pensioner population in the UK will increase from 12million to 20million.
Alistair McQueen, head of savings and retirement at Aviva, said,
"Worryingly, our research shows that less than four in 10 people can confidently estimate the value of their pension savings. This could put our retirement wellbeing at risk as millions either under or over-estimate the value of their pension savings.
"Automatic enrolment has brought pension savings to millions. And the pension freedoms have given us unprecedented choice in how we can use that money when we reach 55.
"But we risk sleepwalking into our retirement if we don't understand how much we have in our pension pots, what those savings might look like as retirement income and how long we need that money to last."
However, Mr McQueen said that the good news is that there is plenty of help available from a wide variety of sources.
