The objectives of this paper are to analyze the mass transfer characteristics during CO2 bubble absorption and diffusion processes in nanofluid with Al2O3 nanoparticles. To analyze the effect of the nanoparticles on the mass transfer enhancement, the surface tension and viscosity of the nanofluids are measured. It is found that Al2O3 nanoparticles enhance CO2 absorption rate and increase the viscosity as high as 11% at 0.01 vol% but the surface tension keeps almost constant. The images of bubble absorption and diffusion are captured by a high-speed camera with the shadow-graph method. It is found that the mass transfer coefficient is enhanced up to 26% at 0.01 vol% compared with pure methanol. (C) 2014 Elsevier Ltd. All rights reserved.