Abstract: Late Carboniferous granite in the Xiao Hinggan Mountains shows magma-mixing characteristics. In the granite mafic magmatic enclaves are well developed. They are mosdy fine-grained dioritic magmatic enclaves. The enclaves are highly varied in shape and size and have clear-cut, vague or transitional relationships with host rocks. It is evident that the mineral assemblage of enclaves is not in balance. For example, xenocrysts of alkali feldspar appear in the host rocks, sometimes rims of dark-colored minerals may be observed, and there also appears acicular apatite, which suggests that the magma mixing of the Late Carboniferous granite in the Xiao Hinggan Mountains is marked by mixing of basic magma and acid magma. This prorides petrographic evidence for the study of the genesis of the granites and also implies that vertical crustal growth probably took place in the Late Paleozoic Jiamusi-Songnen craton.