The paper deals with the experimental investigation on the determination of axial stress-strain relation, the concrete thoroughly made with the lightweight aggregate of coconut shell. Four different grades of coconut shell concrete were used in the experiment. The coefficient of secant modulus and modulus of elasticity and chord modulus variations were observed. The experiment is entirely done with extensometer, stress-strain relations were observed. The empirical equations were finally proposed to describe the stress-strain relation of coconut shell concrete. © IAEME Publication.