We conducted a detailed comparative study on the petrogenesis of three types of granites in the southern Chinese Altai, using a multi-faceted approach including petrology, whole-rock and mineral chemistry, and zircon Hf-O isotopic analysis. The perthite granites and alkaline feldspar granites from Kouan Pluton are peralkaline and aluminous A-type granites, respectively. They formed coevally in an extensional event during the late Devonian to early Carboniferous orogenic period. The peralkaline granites have distinctly high total alkali, FeOt/(FeOt + MgO), incompatible elements, and low Ba, Sr, Eu contents. They are anhydrous and reduced, possessing high zircon εHf(t) of 9.5–14.3 and zircon δ¹⁸O of 5.41–7.81‰. Petrological and chemical analyses suggest that they were formed by extensive differentiation from an enriched mantle-derived alkali basalt. The aluminous A-type granites show chemical features transitional between the peralkaline granites and the Xibodu I-type granites mentioned below. The geochemical and zircon isotopic data (εHf(t) = 8.3–15.1; δ¹⁸O = 6.39–8.70 ‰) imply their derivations from the mixture of evolved alkaline magma and juvenile crustal melts. The Xibodu granites were emplaced later (ca. 270 Ma) and have arc-like trace element signatures, with zircon εHf(t) of 8.0–13.2 and δ¹⁸O of 5.92–7.84 ‰. We interpret that they originated from anatexis of the juvenile lower crust during the post-collisional extension. Some of them show chemical compositions similar to the Kouan aluminous A-type granites such as high alkali, FeOt/(FeOt + MgO), HFSE and REE, which was a result of high fractionation possibly facilitated by the high temperature and volatile contents. Nevertheless, comparisons of field, mineralogical, and geochemical data show that A-type granites are a distinctive group of granites formed from melts with lower H₂O and oxygen fugacity and higher temperature than ordinary granites, while the tectonic setting is not directly related to rock types in nature.