Five newly synthesised biphenyl derivatives were evaluated for their acute contact toxicity (LC50) against rice weevil and honey bee and anti acetylcholinesterase potential (I50) against honey bee, fish, pigeon and rat. Amongst, O,O-dimethyl-O, p-Nitro-biphenyl phosphate was most potent against rice weevil, whereas p-(4-Nitrophenyl) phenyl-N-methyl carbamate against honey bee. Based on I50 values the biphenyl derivatives of phosphoric acid esters were more potent anti acetylcholinesterase (AChE) agents against rat and fish brain AChE while derivative of carbamic esters towards pigeon brain AChE. The anti AChE potency of both groups appear to be of the same order towards bee head AChE.