The present paper deals mainly with chemical composition of pyroxenes which constitute the major rock-forming minerals in the Huangshandong mafic-ultramafic complex.Orthopyroxenes in the Huangshandong complex are exclusively bronzitc, which seems related to host rocks in chemical composition, being rich in "En" in the ultramafic facies and enriched in "Fs" in the hornblende-gabbro facies. Clinopyroxenes vary considerably in chemical composition, covering augite, diopside and enstatite-diopside. In the same host rock, clinopyroxenes contain more TiO2, A1203, Cr203, Ca0 and Na2O but less MgO, FeO, Mn0 and SiO2 than orthopyroxenes.Statistical analysis indicates that from the ultramafic facies to the hornblende-gabbro facies, chemical composition of orthopyroxenes varies from the enrichment of MgO, SiO2 and Al2Os to the enrichment of FeO, TiO2, Ca0 and MnO, whereas that of clinopyroxenes from the richness of A1203, Cr203, Na2O and MgO to the richness of FeO, Mn0 and CoO. There exists linear positive correlation between Fe2+/Mg values of coexisting two pyroxeness; KD values vary in the range of 0.92-3.42, equivalent to KD values of pyroxenes of magmatic origin. Their equilibrium t and P are 947-1157℃ and 0.58-10.58 (0.1 GPa) respectively. Chemical composition of the pyroxenes indicates evidently that their parental magma was tholeiitic magma formed by partial melting of garnet-lherzolite in a plate-tectonic setting of island arc.