A series of blend films of silk fibroin (SF) with nylon 66 were prepared by the common solution cast method. DSC analysis of every blend sample showed a large and broad endothermic peak around 150 degreesC. For SF/nylon 66 samples containing 10 and 30 wt% SF, large spherulites were observed and their melting processes were recorded using a polarizing microscope with hot-stage. Furthermore, a detailed study on 30 wt% SF sample indicated a distribution of two distinct spherulites: large spherulites in part A and much smaller ones in part B. In WAXD pattern, the large spherulites presented new peaks different from nylon 66 or silk's characteristic peaks that were ever reported, while the small ones assumed triclinic form of normal nylon 66. SEM showed that the SF and nylon 66 were nearly miscible in all ratios except that of 50 wt% SF. (C) 2004 Published by Elsevier Ltd.