The effects of Aspergillus fumigatus(AF) and Penicillium citrinum(PC) deterioration of test materials were examined. When the fungi were inoculated to the silk fibers placed on Czapeck agar, malt extract agar and potato agar, they grew best on potato agar which in that context was chosen as a basal medium for deterioration studies. The tensile strength of silk fiber on which AF was grown for 30 days decreased by 28.5% with a concommitant increase in elongation by 40.1%. Silk fabric lost the weight by 4.74%, when inoculated with AF while it lost the weight by 3.37%, when inoculated with AF. When AF and PC were inoculated separately on silk fibers, tensile strength decreased by 76.3% and 56.4%, respectively, with concommitang increases in elingation by 53.1% and 37.8% respectively. The silk was damaged more severely by AF than PC, when they were observed by scanning electron microscope.