This research aims at evaluating the effectiveness of social skills training on two groups: children and children and their mothers in decreasing loneliness and increasing peer acceptance. The sampling method of this study was purposive, two schools among six primary schools of the fourth education area of Shiraz with the same educational, social class, and cultural level were chosen.300students were evaluated by Asher's scale about children's loneliness and the inventory of the peer acceptance.65students with the highest score in loneliness and lowest score in peer acceptance were selected and were randomly put into three groups (i.e two experimental groups and a control group). In this semi- experimental research, the children in both groups were trained during eight one-hour sessions. in the other group children's mother were separately trained in six one-hour sessions. Finally post-test were given and covariance were used for analysis of data. Results from statistical methods, analysis of covariance, revealed significant increase in peer acceptance and significant reduction in loneliness on two groups. Although the average difference among these two groups was high, the comparison of these groups' efficacy wasn't significant. By means of social skills training It is possible for lonely children to make friends and enter to peer group, it causes the reduction feeling of loneliness and increase in peer acceptance among peers. The lack of statistical significance in comparing two groups doesn't refute the clinical importance of this field. it is suggested that parents, specially mothers have an important role in social skills training and children's relationships with their peers.