In this study, first, developmental difference of GMFM(Gross Motor Function Measures) and social maturity was looked at, with regard t o the birth weight and developmental stage of gestation. And second the factors that bare influence on GMFM and the development of their social maturity were looked into. For the examination from March 10 to April 20, 2002, sixty five spastic diplegia cases of children under 8 years old were taken from 5 welfare centers and 4 hospitals in Gyeonggi and Seoul area where they were being treated for the case. As for the study tools, questionnaire, GMFM test, and Social maturity test were used. And general characteristic o f diplegic children and their mothers was calculated in percentage. The findings are as follows: 1) the difference between GMFM and social maturity based on gestation and birth weight of spastic diplegia indicated no significant difference. 2) social maturity test and the gestation of 28 weeks and birth weight of 1,500gm produced significant difference (p<0.05). 3) For children with spastic diplegia, the most predictive variables for Social Age(SA) were the childs age gestation had negative effect and timing of the treatment had the positive effect on social maturity which accounted for 40.0% of the variance. And what had positive impact on GMFM were birth weight and the timing of treatment, telling the importance of the timing of its treatment. So it is thought that timely treatment of the spastic diplegia is necessary to improve the functional activity and social maturity of the patients.