Only caring staff were thought to be more important in a survey of nearly 1,000 parents at 37 nursery schools across the country carried out by the National Foundation for Educational Research.
Recent tragedies such as Dunblane had made families keenly aware of the importance of security, researchers said, but the strength of feeling was nevertheless surprising.
The study, published this week in two NFER reports, also highlighted a need for greater information for parents choosing a nursery school, and urged local authorities and the Government to help publicise the variety of provision parents could choose.
Researchers Caroline Scott and Claudia Davis found three-quarters of parents had learned about places through word of mouth from family, friends or neighbours.
And while 92 per cent visited the pre-school before enrolling their child, almost two-thirds said they had not visited a second place for comparison.
But the security issue arose repeatedly. Asked to select the most important factors in choosing between two similar pre-school centres, 77 per cent cited good security compared to only 73 per cent for good facilities.
"It was also the main thing parents wanted to see improved at their own child's pre-school," Ms Scott said.
"The strength of feeling we met was a surprise. Parents referred to Dunblane and were thinking themselves through the situation - could an intruder gain an access here?
"They didn't always feel pre-school staff were paying attention to the issue."