The disseminated and banded chromites in the serpentinized ultrabasic rocks of the Dacaotan area, East Tianshan Mountains, are helpful to clarifying the characteristics and evolutionary process of the rocks. Some chromites have zoned texture,with rich Al but poor Fe in the core. The geochemical characteristics of the core of chromites, with the data Cr₂O₃ 39.27%~42.65%,Al₂O₃ 24.58%~26.21%,TiO₂ less than 0.20%,FeO 12.18%~18.14%,Fe₂O₃ 0.33%~7.30%, Cr^# 50.6~53.5, Mg^# 53.3~68.2, and Fe^{2 + #} 31.8~46.7, are in accord with the features of ophiolites serpentinite and may be a member of ophiolites. Moreover, the crystallization temperature and pressure of the chromite are estimated to be 1 385℃ and 2.77 GPa on average, respectively, with a formation depth of about 86 km, which is similar to features of the asthenosphere. The oxygen fugacity relative to FMQ buffer is FMQ -4.38~FMQ + 0.63 log units, FMQ -1.15 log units on average. Furthermore,the degree of partial melting of the mantle is estimated to be in the range of 21.04%~21.28%,21.18% on average, in the light of its relationship with Cr^#. These parameters provide some clues to the physicochemical conditions:these peridotites were derived from garnet lherzolites located in the asthenosphere of the upper mantle, and Dacaotan serpentinite was formed in the depleted island-arc setting of supra-subduction zone. The compositional zoning suggests that the peridotites have undergone a thermal path of decreasing temperature and increasing oxygen fugacity.It can be inferred that the mantle peridotites experienced the process from the stage of high temperature and high pressure mantle with lower oxygen fugacity to the thrusting slice stage to reach the crustal surface, where they were subjected to regional metamorphism with higher oxygen fugacity.