Effect of ion temperature on the conditions for existence of solitary waves in a relativistic plasma is studied using Sagdeev's pseudopotential approach. It is shown that the ion temperature puts a restriction on the values of V, the soliton velocity. It is also shown that for small amplitude and cold ions, the present results agree with the existing published results. Numerical solutions of the equation of motion derived from the pseudopotential are obtained to see the effect of ion temperature on the width and amplitude of the ion-acoustic solitary waves.