Mantle xenoliths, with minor garnets, have been found in the Quaternary volcanic rocks in Da Hinggan Mountains. Reaction rims, documenting significant records of mantle dynamic evolution, are common in most of the garnets. Optical photomicrographs and BSE pictures demonstrate three types of reaction rims of garnets, ① coronal rims, a thin layer of 0.1~1 mm enclosing the relic garnet, with a typical mineral assemblage of Opx+Glass, Cpx+Glass or Grt+Sp; ② vein rims, vein-like strips in several 100 μm in width and several millimeter in length, with a typical mineral assemblage of Opx+Glass; ③ microfracture rims, very thin reaction rims of several to several ten micrometers thick along microfractures in garnet, with a typical mineral assemblage of Sp+Glass. On the aspect of petrogenesis, these reaction rims were divided into two types, ① origin of magma/melt reaction with garnet:Some reaction rims have quite different bulk chemical composition from the precursor garnets. For example, K₂O and Na₂O compositions in garnet reaction rims are one or two orders of magnitude higher than those in precursor garnets, indicating that compositions from mantle melts or alkaline magmas were induced to the mineral assemblages of reaction rims; ② origin of isochemical breakdown of garnet:The other reaction rims have nearly the same bulk chemical compositions as the precursor garnet, indicating isochemical breakdown of garnet without any significant chemical compositions from mantle melts or other minerals, especially the vein rims and microfracture rims. Hence two types of garnet reaction rims with quiet different origins were found in Quaternary volcanic rocks in Da Hinggan Mountains. These garnet reaction rims provide evidences of K₂O- and Na₂O-rich melt reactions and mantle refertilizing processes, as well as evidences of evolution of mantle p-T conditions. Studies on garnet reaction rims may light on further understanding on chemical evolution and thermal history of lithospheric mantle in Da Hinggan Mountains.