The studied platinum-gold placer occurs in Quaternary alluvial-diluvial sediments within a piedmont valley of ultrabasic rocks, Northwest China. Several platinum group element(PGE)minerals from the placer were studied under microscope and by electron microprobe and X-ray diffraction analysis, The Os-Ir-Ru minerals include iridosmine, rutheniridosmine, osmium and osmiridium. The Pt-Fe mineral is identified as isoferroplatinum.The studied mineral assemblage is Os-Ir-Ru minerals+ isoferroplatinum+native gold+native silver+chrome-ceylonite+chromite+magnetite+ ilmenite+cinnabar,suggesting that the placer is probably derived from the chrome-bearing ultra-basic rocks.The result of the study provides useful mineralogical data for evaluation of the placer,and also serves as a valuable indicator in the prospeacting for primary PGE deposits related to chrome-bearing ultrabasic rocks in the area.