The use of LiNbO3crystals in nonlinear optical experiments has been limited by the lack of long, high‐quality crystals. We have shown that crystals grown from a congruent composition melt are significantly less susceptible to birefringence variations which in the past have limited the useful phase‐matchable lengths of LiNbO3crystals. Both a birefringence test which directly measures the spatial birefringence of the crystal and a second harmonic generation test were used to evaluate crystals grown from melts of various compositions. Crystals with less than 10−5variation in birefringence over a length of 4 cm have been obtained repeatably when grown from congruent melts.