The study was conducted with 1500 healthy silkworm larvae. There were two treatment groups: control group, without added Bacillus subtilis, and B.subtilis group, with B. subtilis at 2.0×1010 CFU/mL added to the feed. Experimental diets were fed in three phases: 3rd instar, 4thinstar and 5th instar. Furthermore, 3 replications were maintained and 250 silkworm larvae were reared in each replication. Different growth parameters and cocoon parameters were measured at each stage of silkworm. With the aim to investigate the supplemental effects of B.subtilis on growth performances, cocoon quality and amylase activity of silkworm, Bombyx L, we got the following results: (1) In the larval duration of 3rd instar silkworm, average weight gain (AWG) and feed conversion ratio (RFC) were not significantly affected with the use of B. subtilis, but the remaining amount of mulberry leaves (RAML) was significantly decreased contrasting to the blank group (P<0.05). (2) In the larval duration of 4th instar silkworm, adding B. subtilis to the feed could significantly increase the AWG and RFC and decrease of RAML (P<0.05) (3) In the larval duration of 5th instar silkworm, maximum growth parameters level were achieved with silkworm in the experiment group, that the AWG, RFC and RAML, were very significantly affected by adding the B. subtilis to the feed (P<0.01). (4) Pupa weight (PW) and cocoon weight (CW) were significantly affected by the added B. subtilis (P<0.05). Other cocoon parameters, such as frison weight (FW) and average cocoon weight (ACW), were more pronounced increased than the blank group (P<0.01). (5) The proteinase activity in middle intestine was higher than that of the blank group (P<0.05). Collectively, the results indicated that adding B.subtilis to the feed of silkworm had positive effects on growth performances of the Bombyx mori L. apparently.