AbstractPain is composite distressing sensory experiences that include several elements like time, space, intensity, emotion, perception and motivation. Analgesics are the Pharmacological agents; acts selectively for relieve pain by acting on the central nervous system or peripheral pain biochemical interactions without causing more effect on consciousness. Analgesics may come under narcotic or non-narcotic category. The evolutionary study of pain on animals arises ethical, philosophical and technical problems. Philosophically, theproblem of study the pain on animals is that pain cannot be observed directly in animals but can only be accessed by measuring the animal responses to nociceptive stimuli. The perceive reactions are always motor responses varyingfrom spinal reflexes to complex behavior. The animal models hired for screening of analgesic agents, include Pain state models depends thermal stimuli, mechanical stimuli, electrical stimuli and chemical stimuli as mean of accessing. The neuronal basis of most of the above laboratory models can’t deeply explained, however their usage is profitable in predicting analgesic activity of newly discovered chemical agents.