Silkworm larvae were fed on leaves of mulberry trees)Morus nigra) treated with three different concentrations (3%, 6% and 9%) of each yeast Saccharomyces cerevisiae and soybean. The highest weight of fifth instar larvae were when larvae fed on leaves treated with yeast than soybean at 9% concentration. The maximum total weights of consumed and digested leaves by larvae of fifth instar when larvae fed on leaves of M. nigra, treated with yeast at 9% concentration compared with soybean and control. The maximum efficiency of conversion of ingested and digested food to body substance was also obtained in fifth instar larvae fed onleaves treated with yeast at 9% concentration compared with soybean and control. The highest weights of cocoons and cocoon shells when the larvae fed on leaves of M. nigra, treated with yeast at 9% concentration compared with soybean and control. The highest fecundity occurred when larvae fed on mulberry leaves treated with soybean compared with yeast and control. The egg hatch was not affected by different treatments and different concentrations.