Abstract: Determination of 42 elements in ultra ine geological samples by inductively coupled plasmamass spectrometry with pressurized acid digestion was reported in this paper. Some parameters influencing the analytical accuracy and precision, including particle size of the samples, conditions of the digestion and sample mass tested were optimized. The results indicated that when ultra ine samples (<30 μm) was used the reproducible results could be obtained even if the sample mass tested was reduced to 2 mg and acid used for sample digestion was reduced to less than 0.5 mL. The method fully takes the advantage of high sensitivity of ICP-S and provides he advantages of more efficiency, low cost and environment riendly.