The effects of spinning conditions on the tangent modulus-strain curves have been studied using isotactic polypropylene(iPP) mononlaments. The tangent modulus-strain curve, which is derived from the first derivative of the true stress-strain curve, showed three distinct peaks. The tangent modulus of the first and the second peak in the tangent modulus-strain curve were increased as the draw ratio and the spinning speed were increased. The tensile strain of the first peak had little dependence on the process conditions, however, that of the second peak decreased above the natural draw ratio. The spinning conditions had little effect on the tangent modulus of the third peak, while the tensile strain of the third peak decreased as the draw ratio was increased. The variation of the isotactic helix content in iPP monofilament, determined from the FIIR spectra, was in agreement with that of the tangent modulus-strain curve with the tensile strain.