Abstract: Sampling behavior of multielements in a stream sediment matrix was studied with sample sizes ranging from several hundred mg down to sub-ng by using a combination of INAA-PIXE-SRXRF. For accurately weighable sample sizes (>1 mg), INAA was used. On the condition of sampling sizes unable to be accurately weighed (<1 mg), PIXE and SRXRF were used with the effective sample sizes being estimated according to the ranges of incident particles and absorption coefficients of characteristic X-rays. Preliminary results show that the sampling uncertainties for 16 elements are better than 1% on the sample sizes above 1 mg by using INAA, those for 7 elements are better than 1% on the sample sizes of sub-mg by using PIXE, and for 3 elements Cu, Fe, and Rb, they are better than 10% on the sample sizes equal to or larger than 7.5, 9.6, 42.4 ng, respectively. This study may pave the way to preliminary establish a new kind of CRMs suitable for quality control of solid sampling microanalysis.