Small business owners’ biggest fear? Not having the money to retire, says a new study.

Nearly two-thirds of small business owners fear outliving the money they need to retire, according to a poll from the Guardian Life Small Business Research Institute

Many of the 1,433 small business owners surveyed expect to live well into their retirement years, with one in three saying they plan to retire older than 70. Less than half (45 percent) felt very or fairly well prepared for retirement. Nearly one in seven plan to work part-time in retirement while 10 percent expect to work full-time.

Patricia G. Greene, a professor of entrepreneurship at Babson College, points out that "retirement" may not mean the same thing to small business owners as it does to people who have spent their lives working for other people. "In many cases, small business owners keep working because they love what they are doing and don't see the point of retiring," Greene said in a statement.

Mark Wolf, director of the Guardian Life Small Business Research Institute, says the traditional concept of retirement isn’t realistic for small business owners. "They feel that keeping their business going and working in it full- or part-time are essential steps to provide a continuing income stream to supplement savings," he said.

Nearly two in five (39 percent) said they expect to go back and forth between periods of work and periods of leisure. Six percent are planning to do some volunteer work and four percent plan to start another business.

Given the lack of faith most small business owners have that they’ll be able to stop working, it’s perhaps not surprising that only one third of them have a succession plan in place. Just under a fifth (19 percent) said they plan to create one in the next year.

About a third are counting on proceeds from the sale of their business for retirement. (Why are sales of small businesses on the rise? Click here.)

Said Douglas Dubitsky, the vice president of product management in the retirement solutions division of the Guardian Life Insurance Company: "Depending on market conditions, the value and salability of many businesses have significantly declined, reducing their potential contribution to a retirement plan."