New nonlinear optical crystals GdCa4O(BO3)3 grown by the Czochralski method in a platinum crucible under air atmosphere are reported in this paper. The growth mechanism is a typical two-dimensional nucleation layer growth. The twin and inclusion defects of this crystal are observed using optical microscopy. The incidence of twinning is in good agreement with Hurle's model. The approaches to reduce and eliminate the defects are presented.