Biomax (R) is a biodegradable plastic with high thermal resistance. In this study, Biomax. fiber was hydrolyzed at pH 3.0-10.5 for up to 4 weeks at 80 degrees C. The degradation of the fiber was evaluated based on the degradation products, molecular weight, and scanning electron microscope (SEM) observations. The largest amounts of degradation products were obtained with an alkaline carbonate buffer (pH 10.5). The molecular weight of the Biomax (R) fiber decreased remarkably in dilute sulfuric acid (pH 3.0); specifically, it decreased to 23% of the original molecular weight after 1 week. SEM images agreed well with the change in molecular weight. These results reveal remarkable differences between the degradation behavior in alkaline and acidic solutions.