Nutritional values of mulberry leaves greatly affected growth and development of the commercial silk worm, Bombyx mori L. larvae and in turn silk production. Therefore, larvae of the last two instars were fed on treated leaves by dipping them in royal jelly solution at the rate of 5 g in 200 ml distilled water before offering them to larvae as food. This treatment increased the weights of  the fourth and fifth instar larvae, weights of fresh cocoons, pupae, cocoon shell and reeled silk filament. The weights of ingested and digested treated mulberry leaves as well as approximate digestibility and efficiency of conversion of ingested and digested food to body substances in the fourth and fifth instar larvae were also increased as compared with those of larvae fed on untreated mulberry leaves. Feeding the last two instar larvae on treated leaves elicits favourable response in improving the commercial quantities of silk fibre and can be used in Sericulture for yield enhancement.