Optical transmission, refractive‐index, and nonlinear optical properties of single domain PbTiO3have been measured between room temperature and the Curie temperatureTc. The second‐harmonic coefficientd31is found to be the highest for any room‐temperature ferroelectric. Since the birefringence is small (approximately 0.008), phase‐matched SHG is not possible, but nondegenerate three‐frequency mixing should be possible. The Miller &dgr; coefficients are analyzed in terms of Jerphagnon's formulation and poor agreement is observed.