This study set out to research preference of material color, to analyze the impacts changes of the depression an more effective of Horticultural therapy program for the old adults. The subjects were made out of the old adults who were taken care at 'Daeduk Senior Welfare Service Center' located in Namgu, Daegu Metropolitan City. The experiment was conducted once a week form Aug. 9 to Nov. 1, 2005, total in 13 times. To estimate the research subject's remedial value, GDS-K(Geriatric Depression Scale in Korean) was implemented before and after performing a horticultural therapy program, and each time a color preference for program key materials was examined. The evaluation is as follows : GDS-K evaluation indicated that the average point for entire research subjects prior to its implementation presented 23.4, while it was 16.6 with 7 drop after its implementation, which consequently implied a gradual decrease in melancholy and statistically showed a significant different(P<.05). Findings on the survey regarding a color preference for key materials revealed that cut flower, artificial flower, and colored stone, and moss preferred red color the most, while seed liked green color the most and floral form cared for pink the most. The findings drawn so far indicated that the horticultural therapy using bright and clear colors provided a positive impact for old people's melancholy. I conclude that it would be helpful for changing one's mood and improving an melancholy, to let horticultural therapy programs use their materials mainly with bright and clear colors, so as to make deeply-melancholy old people feel refreshed.