Half of those surveyed by Research Plus for Standard Life found that just 41pc of people own a private, company or work scheme pension.
Almost half of adults surveyed said they couldn't afford to save into a pension.
The people most likely to have a problem saving for a pension are between 45 and 54, it found. But experts said this was the time people needed to save most, as they were nearer retirement.
Jim Connolly, head of pensions at Standard Life, said: "Pension saving is a good thing and makes people feel much more confident about their finances.
"It reduces people's stress levels if they are making provision for a decent retirement.
"For those fortunate enough to have a few quid extra each month, the question is can they afford not to save into a pension if they want to enjoy their retirement?"
Men are far more likely to have a pension than women – almost half of men own a pension compared with less than a third of women.
Many private sector workers who do have a pension have only built up small pension pots, experts said. The weekly state pension payments amount to €230.
The Government is considering an auto-enrolment pension scheme for those who do not have a private retirement fund.
Workers would be able to pay a fixed amount relative to their income into one national – or possibly private – scheme over the course of their working lives.
There would be additional matching contributions from their employer and the Government through tax relief.
But no date for the introduction of this scheme has been announced.
A review of Ireland's pension system by the OECD, published in April, backed compulsory pension savings as the most effective way to increase the adequacy of retirement savings, with auto-enrolment branded a more costly and second-rate policy.