Studies on the effect of sublethal concentration (5.0 mg/litre) of a weedicide, Linuron were made for the changes in some haemato-biochemical parameters in an air breathing teleostean fish, Clarias batrachus (Linn.). In control group of fishes the values of blood glucose, plasma protein and blood urea were 59.542, 12.04 and 30.92 mg/100ml of blood respectively. The exposure of fishes to sublethal concentration of Linuron (5.0ppm) for different hours (24, 48, 72 and 96 hrs.) caused significant increase in blood glucose and blood urea and considerable decrease in plasma protein. The reason for such changes has been discussed in this paper.