The magnetic, thermal, and transport properties of martensitic phase transformation in single crystal Co5Ni2Ga3 have been investigated. The single crystal Co5Ni2Ga3 shows martensitic transformation at 251 K on cooling and 254 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve, and temperature-dependent thermal conductivity curve are observed at martensitic transformation temperature (T (M)). Negative magnetoresistance due to spin disorder scattering was observed in Co5Ni2Ga3 single crystal at all temperature range. The temperature-dependent negative magnetoresistance shows a peak at T (M), which indicates that the spin disorder increases in the process of phase transition. Co5Ni2Ga3 sample exhibits a temperature dependence of thermal conductivity kappa(T) (d kappa/dT > 0) due to electrons being above temperature 100 K.