Abstract: A method for direct determination of niobium and tantalum in fused rock glasses by argon fluoride 193 nm excimer laser ablationinductively coupled plasma mass spectrometry was reported in this paper. NIST SRM 612 was used as external calibration standard and 29Si as internal standard to correct signal drift, difference in transport efficiency and sample yield. The detection limit of the method are 0.003 μg/g for Nb and 0.006 μg/g for Ta. The method has been applied to the determination of Nb and Ta in National Geological Reference Materials and the results are in agreement with the certified values with precision of less than 10%RSD (n=11).