The distribution of Penaeus monodon baculovirus (MBV) in different parts of mid2gut gland in juvenile and adult shrimp Penaeus monodon was studied by light microscopy. The mid2gut gland of Penaeus monodon can be divided into five parts including head part , subhead part , mid part , subtail part and tail part. The cells of mid2 gut gland can be divided into E cell , R cell , B cell and F cell . The E cell was the main cells of the head part and the tail part. R cell was the main cells of the subhead part , the mid part and the subtail part. In the cases that infected lightly with MBV , only R cell , B cell and F cell were infected. In the cases that infected severely with MBV , besides R cell , B cell and F cell , E cell also was infected. Both juvenile and adult P. monodon , MBV distributed mainly in the mid part of mid2gut gland and especially in the middle of mid part . The farther apart from the mid part , the lower the MBV infection rate was.