Abstract: Two sample preparation procedures (Aqua regia and HNO3-HClO4-HF mixture acid) were used to dissolve the National Standard Reference soil and stream sediment samples and arsenic in the sample solution was then determined by atomic fluorescence spectrometry (AFS). The detection limit of the method for As was 0.02 mg/kg. The analytical results from both sample preparation procedures were in agreement with certified values, showing that these sample preparation methods can satisfy the requirements of arsenic determination in soil and stream sediment samples and aqua regia dissolution procedure was better than the other one when only arsenic is determined. For multi-element analysis (including As), HNO3-HClO4-HF mixture acid procedure is recommended.