Abstract We carried out the damage test of DAST crystals due to identify the causes of laser damages. DAST laser damages were classified into two regions; surface and bulk. The smooth surface tended to suppress the surface damage. As for the bulk, crystal defects such as twin boundary and narrow-line defect (NLD) were the main causes of bulk damages. Twin-free and NLD-free crystal showed high damage tolerance (over 2.8 GW/cm 2). Growing in the low-supersaturated solution and introducing the solution stirring were effective to obtain DAST crystals with high damage tolerance.