The effect of radiation-induced disordering in a nuclear reactor (fast neutrons fluence Phi = 5cdot10^{19} cm^2, T_{text{irr}} = 340 K) on resistivity rho, superconducting transition temperature T_C and upper critical field H_{C_2} of polycrystalline MgCNi_3 samples was investigated. It was found that T_C decreases under irradiation from 6.5 to 2.9 K and completely recovers after annealing at 600 ^circC. Temperature dependences rho(T) are characteristic of compounds with strong electron-phonon interaction. The dH_{C_2}/dT behaviour testifies to a considerable decrease in density of electronic state at Fermi level N(E_F) in the course of disordering.
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