The leaves of four mulberry varieties PFI-1, PFI-2 Karyansuban (Korean) and a Japanese hybrid were biochemically analyzed and fed to a Japanese silkworm variety to study their effect on its development at different stages especially on economic cocoon characters. The results show that mortality of larvae and pupae was low and the effect of PFI-1 and PFI-2 was significant on economic cocoon characters of the variety. The chemical analysis of these varieties showed that protein contents of PFI-1 and PFI-2 were higher then in Japanese hybrid and Karyansuban varieties and hence gave better cocoon shell ratio. The cocoon quality did not show much difference and the percentage of good quality cocoons was 89.5.