[Objectives]  To investigate the effects of adding melamine (MEL) to mulberry leaves on the growth and serum biochemical indices of silkworms, and thereby reveal the metabolic pathways by which ingestion of a nonlethal dose of MEL produces toxic effects in this species. [Methods]  600 newly exuviated 5th instar larvae of approximately the same size were randomly divided into four groups, each group having 3 replicates of 50 silkworms (25 males and 25 females). The control group were fed fresh mulberry leaves whereas the three treatment groups were fed fresh mulberry leaves to which one of three nonlethal doses (10, 15 and 20 mg/kg) of MEL had been added. Monitoring of phenotypic and serum biochemical indices began 5-days after silkworms had begun feeding. [Results]  The addition of MEL slowed the relative growth rate of larvae, significantly so (P<0.05) in the 20 mg/kg MEL treatment group. Glycometabolism and haemolymph levels increased with MEL whereas blood lipid content declined. The addition of MEL had no obvious effect on xanthine oxidase and uric acid content. [Conclusion]  The addition of melamine to mulberry leaves significantly affected the growth, carbohydrate metabolism and lipid metabolism, of silkworm larvae, but appeared to have little effect on their uric acid metabolism.