The decreasing productivity of silkworm cocoon is caused by attack of bacteria, fungi, protozoa and virus. The research was aimed to isolate of suspected pathogenic and biological control bacteria from damage and healthy pupae of golden silkworm (Cricula trifenestrata Helfer) and to do in vivo test of the bacteria toward 4th instar larvae of C. trifenestrata and mulberry silkworms, Bombyx mori Linn. The isolate UPC 60 was suspected as pathogenic bacteria due to cause the mortality of silkworms larvae. The bacteria UPC 40 and UPC 71 were selected as biological control bacteria which had capability to reduce the mortality of silkworms about 56.67 and 43.33%, respectively. Based on 16s RNA gene the bacteria UPC 40 had 97% identity with Alcaligenes faecalis, bacteria UPC 60 had 97% identity with Aeromonas dhakensis and bacteria UPC 71 had 98% identity with Pseudomonas stutzuri. The biological control bacteria showed antagonistic activity toward the pathogenic bacteria. The outcomes of the research that the biological control bacteria expected to be used to reduce pathogenic bacteria in the maintenance of silkworm so that the production and quality of silk yarn can be improved.