The effects of environmental temperature during the early development of seeds on the structural characteristics of the endosperm starch were investigated using near-isogenic lines of rice plants (Taichung 65, waxy), grown under temperature controlled conditions. High performance gel permeation chromatography (HPLC) demonstrated that Pseudomonas isoamylase-debranched amylopectins of rice plants grown at lower temperature (25 °C) contain increased amounts of short chains and decreased amounts of long chains as compared with amylopectins obtained from rice plants grown at higher temperature (30°C). By high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) of isoamylase-debranched amylopectins it was detected that the amount of unit chains with degree of polymerization (DP) 6 and 11-13, in the amylopectin of rice plants grown at lower temperature (25°C) had significantly increased and the amount of unit chains with DP 8, 22-24 and 29 had significantly decreased, as compared with the amylopectin of rice plants grown at higher temperature (30°C ). It was confirmed that the environmental temperature between 5 and 10 d after pollination strongly influenced the structure characteristics of the endosperm starch of rice plants.