The spin structure and polarization characters are the dominant aspects in the physical properties of manganite systems with colossal magnetoresistance effect. In this paper, a series of Mn-site doping samples La2/3Ca1/3Mn1-xCoxO3 (0≤x≤0.15) have been prepared with Co ion which has mult-spin states. The structure and transport properties of this system have been systematically investigated. The results showed that all the samples show good single phase and the lattice parameters decrease with the increasing of doping concentration x. The abnormal transport properties are induced by Co doping. To be specific, the resistivity exhibits two metal_insulator (M—I) transitions (double peak effect). Both high temperature peak (TMIH) and low temperature peaks (TMIL) shift to low temperature end with increasing x. While the TMIH shifts to high temperature, the TMIL is almost unchanged under the external field. The corresponding peak values of resistivity show strong dependence on the external field and Co doping concentration x. All the peak values of resistivity increase with the increase of x, and the low temperature peak value seems more sensitive than the high temperature peak. Compared with the magnetization properties, it could be concluded that, the high temperature peak is related with the undoped M-I transition, and the abnormal behavior of low temperature peak has certain relationship with the oxygen vacancy and high spin state induced by Co3+ substituting Mn4+ in the present system.