This paper presents an experimental investigation of the flow boiling heat transfer characteristics of CO 2 in a horizontal micro-fin tube at saturation temperature of −30 °C. The test tube, made of copper, with outer diameter of 7.94 mm, was uniformly heated ohmically by high electric current through a transformer. The tests were conducted at mass and heat fluxes, ranging from 100 to 250 kg m −2 s −1 and 10–25 kW m −2 , respectively. The new experimental data from these tests for varying conditions is provided in Appendix 1 for future research. The experimental data shows that h tp increases with vapour quality until dryout, and decreases with saturation temperature, while heat flux has more pronounced effect on h tp , suggesting the dominance of nucleate boiling. Furthermore, predictions from several empirical correlations disagree with the current CO 2 experimental data in the micro-fin tube. [11] and [4] correlations predict with deviations of up to ±50%.