This study was inquired into the effect of horticultural therapy on the self-concept and personality development of institutionalized children. It conducted a weekly horticultural therapy program 17 times from March 22 to July 12, 2006 on institutionalized children using an H child institution located in Youngcheon-city, Gyeongsangbuk-do. It made a comparative survey of the effect of horticultural therapy with self-concept scale, child behavior checklist (K-CBCL) and sociality scale before and after conducting the program. The results of this study were as follows: First, analysis of self-concept scale showed that the average value increased significantly as 110 after execution of horticultural therapy into 100.5 before that (p<.05). Particularly, there was a significant difference in the moral self of subordinate sphere (p<.001). Second, analysis of K-CBCL showed that there was a significant difference in the attention and concentration (p<.05). Third, analysis of sociality scale showed that the average value was increased as 73 after execution of horticultural therapy into 64.5 before that, which there was a significant difference in the sociality (p<.001).