This study was carried out to investigate the effect of mulching materials on the fruit quality of Miyagawa Early Satsuma Mandarin in the plastic house. The mulching time was 10 days after water irrigation breakage. The mulching materials used, in order of decreasing light reflectivity, were; micro-perforated vinyl sheets, non-woven fabric film, porous black P.E. film and non-mulching(control). Peel coloration by a values in the treatment of the micro-perforated vinyl sheets showed a 6.93 increase over the control group. The a/b values were similar to this trend, but there were no significant difference among the mulching treatment groups. The glucose level of fruit juice was much higher in the mulching treatment groups as compared with that of the control group, but there was no significant difference among the mulching treatments. Fructose content in the treatment of the micro-perforated vinyl sheets a 0.31mg%.m $L^{-1}$ increase over the control group. This group also showed a 1.36%.m $L^{-1}$ increase in sucrose and a similar increase trend in total sugar. The Brix value was 0.9 $^{circ}$Brix higher in the micro-perforated vinyl sheet group(12.4 $^{circ}$Brix) than in the control group(11.5 $^{circ}$Brix) which result in a significant increase with micro-perforated vinyl sheet usage. However, the acidity level did not differ significantly among mulching treatments.