In the present work an attempts has been made to study the effect of L-thyroxine (T4) and Thiouracil (Tu) on somatic (S.G.R.) and linear growth rate (L.G.R.) in an air breathing freshwater siluroid fish, Heteropneustes fossils (Bloch). The treatment of L-thyroxine (at physiological dose) brought about significant increase both in somatic growth rate as well as linear growth rate while the effect of thiouracil was contrary to this. The details have been discussed in this paper.