BACKGROUND: Children are exposed to dangers of loneliness. This problem is associated with violent aggression, depression and anxiety. Therefore, the effect of peer relationship and family function on children's loneliness was investigated in this study. METHODS: This study was based on the survey administered to 198, 5th and 6th grade students of five elementary schools in Seoul, Korea, in May, 2007. We investigated family function, peer relationship and children's loneliness by self-rating using the Smilkstein's Family APGAR, Peer Environment Scale and Children's Loneliness Scale. The collected data were analyzed with SPSS ver. 12.0. RESULTS: Comparison group of children with different gender showed significant difference in the peer relationship, especially emotional support. On the other hand, data showed children's loneliness and family function were not affected in male or female children. Group of children with more intimate relationship and healthier family function reduced children's loneliness. Peer relationship and family function had the greatest infl uence on children's loneliness. CONCLUSION: Group of children with more intimate relationship and healthier family function reduced children's loneliness. Accordingly, family physicians should heed to their family function and know that it has an effect on children's emotions.