YbxY1 xAl3 (BO3) 4 (x 0:1, 0.07 and 0) crystals have been grown by the flux method. The growth defects of YbxY1 xAl3 (BO3) 4 crystals were detected by X-ray topography. It is found that the perfection of YbYAB crystal with low Yb dopant is better than that with high Yb dopant. In Yb0. 1Y0. 9Al3 (BO3) 4 crystal, growth bands, growth boundaries, grown-in dislocations and inclusions were observed. However, the densities of growth defects for Yb0. 07Y0. 93Al3 (BO3) 4 and YAl3 (BO3) 4 are low and no obvious inclusions are observed in these crystals. In addition, growth twins were detected in YbxY1 xAl3 (BO3) 4 crystal by using the chemical etching method. It is found that the rowth twins occur frequently in Yb0. 1Y0. 9Al3 (BO3) 4 crystal whereas no growth twin appears in YAl3 (BO3) 4 crystal. Based on the experimental observations, the formation mechanism of growth twins is discussed. In the meantime, the e ective measures for reducing the growth twins and defects are proposed.