In 2008, an international survey on obesity among first-graders and its risk factors was performed in Lithuania. The objective of this study was to assess physical activity of first-graders during leisure time according to family socioeconomic status. The study was performed in Siauliai region schools selected randomly in 2008. The anonymous questionnaires were distributed among 630 first-graders and filled out by 515 parents (response rate was 81.8%). It was showed that physical activity of first-graders during leisure time is insufficient. More than half of them (60.4%) did not attend sports or dancing clubs; children spent much time passively watching TV or playing on a computer. Mostly children watched TV for 2 hours on workdays (45.1%) and for 3 hours or more on weekends (41.4%). Mostly children spent about an hour per day playing on a computer: one-third of first-graders spent it on workdays; during weekends, the percentage of children spending about an hour per day playing on a computer was lower (28.5%). One-third of first-graders (36.9%) spent their leisure time outside for 3 or more hours on workdays and 87.1% on weekends independently of parents' educational level, income, and place of residence. The associations between family socioeconomic status and physical activity of children were observed. The lowest percentage of children attending sports or dancing clubs and playing computer games was seen in low-income families and families where parents had low educational level. They spent more time outside (on workdays) compared with those children whose parents had university education and high income. Fewer first-graders from families living in villages than those living in cities attended sports or dancing clubs and played on a computer, but more of them spent leisure time outside.