Histomorphology of the cerebral ganglion of a penaeid prawn P. monodon has been studied by means of classic neurosecretory staining techniques. Three kinds of neurosecretory cells namely A, B and C are distinguished on the basis of their shape, size and tinctorial characteristics of the cytoplasmic inclusions. Heterogeneous distribution of neurosecretory cells in five major groups like B₁, B₂, B₃, B₄ and B₅ has been discussed in relation to the phylogenetic status of P. monodon. Further occurrence of deeply stained tiny cell cluster at the mid-ventral plane of the ganglion is abo reported. Intracerebral axonal tracts leading to optic lobe suggests dispatch of neurosecretory material/cellular products through axonal processes and from the body of secretory neurons as well.