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 (TM). 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 TM, which indicates that the spin disorder increases in the process of phase transition. Co5Ni2Ga3 sample exhibits a temperature dependence of thermal conductivity κ(T) (dκ/dT > 0) due to electrons being above temperature 100 K.