Diseased larvae of silkworms were collected from different rearing areas of Pakistan and Azad Kashmir in 1975-76. Nuclear polyhedrosis virus was identified as one of the causal agents responsible for the death of millions of silkworm larvae in Pakistan and Azad Kashmir. Histopathological studies showed that the nuclei of adipose tissues, tracheal membrane, dermal cells and blood cells developed polyhedral bodies within a week after infection. Nuclear polyhedrosis virus multiplied rapidly and finally occupied the whole cell. Due to rapid increase in number of nuclear polyhedrosis virus, the cells and finally all the tissues disintegrated, resulting in death of the individual. Nuclear polyhecrosis virus infection in silkworm caused heavy losses to poor Sericulturists.