The proton magnetic resonance spectra of 4-cyanophenyl 4′-hexyloxy benzoate (CPHOB) were measured from room temperature to 380K. It was found that the transition temperature from solid to nematic phase was Tｓｎ=347K, and the transition temperature from nematic phase to isotropic liquid Tｎi=359K. The temperature dependence of its order parameter was evaluated. Its mechanism of proton spin lattice relaxation was discussed.