The growth defects in Yb:YAG crystals were investigated by transmission synchrotron topography and chemical etching. The etch pit patterns on three low-index planes (111), (110)and (211) were obtained. It was found that growth striations, core and dislocations were the main defects in Yb:YAG crystal. The dislocations in Tib:YAG mainly originated from seed, impurity particles and inclusions, and seed-crystal interfaces in the initial growth period. The dislocations usually propagate along a path perpendicular to the growth interface. Therefore, in Yb:YAG crystals grown with a convex solid-liquid interface, the dislocations will be decreased or eliminated.