The influence of processing conditions during melt extrusion on the degradation of poly(L-lactide) (PLLA) has been investigated. PLLA polymer was processed by melt extrusion in a double screw extruder at 210 and 240 degreesC. For each extrusion temperature, two screw rotation speeds, 20 and 120 rpm, were used. To investigate the influence of moisture on the thermal degradation during processing, the PLLA granules were dried at 100 degreesC for 5 h and then either extruded directly or conditioned at 65% RH, 20 degreesC for 24 h prior to extrusion. The results show that a decrease in molecular weight measured as number-average (M-n) molecular weight occurs for all combinations of process parameters used. At processing temperature of 210 degreesC, the change in molecular weight for the dry granules was shown to be dependent on the residence time (i.e., screw rotation speed) in the melt. By changing the screw rotation speed from 120 to 20 rpm at 210 degreesC, M-n decreased from 33,600 to 30,200 g/mol. When the processing temperature was increased to 240 degreesC, the dry granules showed an M-n of 25,600 and 13,600 g/mol when extruded at 120 and 20 rpm, respectively. M-n for the conditioned specimens extruded at 210 degreesC was 18,400 g/mol when processed at 120 rpm and 12,300 g/mol at 20 rpm. When processed at 240 degreesC, 20 rpm, M-n is independent of whether the granules were dry or moist prior to extrusion. It is probably due to the fact that the degradation at 240 degreesC is so extensive that the presence of moisture in the polymer does not contribute further to the degradation process. The stress and strain at break decreased due to degradation and were dependent on the molecular weight of the samples.