In this research the effect of family based Developmental early intervention programs on motor skills of down syndrome children, have been investigated. The research question was raised as whether the family based developmental early intervention, has sufficient influences on the motor development of the children aforementioned in their lying and rolling, sitting. Crawling and standing positions. The research has been done on a single subject basis which includes experimental methods. The research population was all chosen from children with Down syndrome who had referred to "zafar rehabilitation center". 8 children were selected from this center with the common following qualifications: 1) All were involved with Down syndrome 2) All were under 2 years of age. 3) None of them had the history of physical defects like cardiac in sufficiency in accordance with the neurological examinations. 4) They were all chosen on the basis of their pretest scores in GMFM scale. The research scale is GMFM -88 (Russell et ai, 2001).this scale has been compiled for the evaluation of gross motors in children with CP and is up to 90% valid and reliable. To evaluate the effectiveness of trainings from the extracted data the "effect size" was utilized. Means in the four aforementioned positions (lying and rolling, sitting, crawling and standing), histograms and, polygonal statistical methods were applied to describe the statistical acquired information. The finding of this research in experimental group in comparison with the control group were as follow respectively: 1) the first highest mean observed in the lying and rolling position in post test (2.29) 2) the second highest mean observed in the crawling position in post test (2.28).3) The third highest mean observed in the standing position in post test (1.61).4) The last highest mean observed in the sitting position in post test (1.55). Since all the post test means were elevated in comparison with pretest means, it could be strongly mentioned that interventions have been effective. On the other hand the highest effect size were observed in the following items respectively: 1) the first highest effect size was observed in crawling position (0.95), the second in sitting position (0.36), the third in lying and rolling(0.35)and the last in standing position (0.34) . At the end, due to the fact that the effect size was 0.50 in the whole in experimental group, it can be asserted that the family based developmental early motor intervention programs, can be drastically effective in the improvement of motor development in children with Down syndrome between the ages of 0-2 years.