The purpose of this study was to determine effects of horticultural therapy program on the mentally retarded juvenile's dexterity and adaptive behavior for vocational rehabilitation. For the mentally retarded juvenile, horticultural therapy program may be opportunities to improve physical integration, coordination, and dexterity, resolve anxiety and stress and set up good relationship with others, making a better human life. Also it provides the opportunities of vocaitonal rehabilitation. To perform the study, the subjects consisted of the mentally retarded juvenile in the B School, Bucheon. Maximizing the effect of horticultural therapy and considering characteristics of the mentally retarded juvenile, horticultural programs were applied to them for 44 sessions, 3 sessions per week and 50 to 60 minutes each session and limited to small group. To investigate the effects of horticultural therapy program on vocational rehabilitation of the mentally retarded juvenile, the researcher carried out the purdue pegboard test, adaptive behavior scale, and psychoscial and emotional behavior test to determine their the dexterity and adaptive bahavior. Based on results form the test and analysis, the research could reach the following conclusion; horticultural therapy programs were effective in promoting the mentally retarded juvenile's physical dexterity, especially both hands and assemble. Also, horticultural therapy programs were benefit to elevating the mentally retarded juvenile's adaptive ability, especially psychoscial behavior. In summary, horticultural therapy programs improved the dexterity and adaptive bahavior for occupational adaptive skill and the vocational rehabilitation of the mentally retarded juvenile in horticultural field is expected.