Silkworm Bombyx mori is an economical insect. Due to the centuries of domestication, it has lost its natural resistance and susceptible to different types of diseases, which leads cocoon crop loss. The major diseases affecting the silkworm are pebrine, flacherie, grasserie and muscardine, which is causing around 27-35% cocoon crop loss. Among these diseases muscardine is one of the contagious disease. It occurs mainly in the rainy and winter season, which is the favorable season for silkworm rearing and in total crop loss around 10-40% crop loss is occurring due to muscardine. Haemolymph is dynamic and life saving fluid which was closely related to all the metabolic activities of the organism. The progress of the fungal pathogen Beauveria bassiana can be monitored by studying the degree of variation in several functions, haemocyte population dynamics and biochemical constituents in the haemolymph, as the fungal pathogen confines to haemolymph till the silkworm larvae approach death. Knowledge on the haematological, biochemical, nitrogenous waste products and enzymatic changes, due to infection by the fungal pathogen in the larvae of Bombyx mori will be useful for evolving suitable prophylactic and control measures against the disease to enhance qualitative and quantitative cocoon yield parameters.