Bastn(a)site is widespread in alkali granite,carbonatite and REE ore deposits.The U-Th-Pb ages of bastn(a)site can constrain the mineralization age.Currently,the lack of suitable in situ analysis reference material is the major obstacle of bastn(a)te U-Th-Pb geochronology.In this study,the matrix effects of U-Pb and Th-Pb age determination in bastn(a)site using glass NIST 610 as the external calibration reference were evaluated with the 193-nm excimer LA-ICP-MS analysis in normal and additional gases laser ablation modes.The obtained U-Th-Pb ages of bastn(a)site were approximately 7-11％ lower than their reference values in the normal analytical mode (without additional gas).Fortunately,the determined systematic age biases in U-Th-Pb dating were significantly reduced (less than 1-2％) with the addition of water vapor within the ablation chamber.This reduction may be attributed to the observed significant suppression of 206pb/238U and 208pb/232Th downhole fractionation in both NIST 610 glass and bastn(a)site by introducing a small quantity of water vapor in the ablation chamber.In addition,the obtained 206pb/238U and 208pb/232Th ages of bastn(a)site K-9,LZ1384,and MAD809 showed great consistency with their corresponding recommended values.The obtained results show that accurate and precise U-Th-Pb ages of bastn(a)site can be simultaneously obtained by using glass NIST 610 as the primary calibration standard in 193-nm LA-ICP-MS with the water vapor-assisted method.This simple and effective water vapor-assisted non-matrix-matched laser ablation method helps to promote the geological application of bastn(a)site U-Th-Pb geochronology.