Haze can cause serious atmospheric pollution affecting air quality, human health and even global climate. In order to investigate aerosol columnar size distribution and water uptake during haze evolution, we analyse ground-based observations during an extreme winter pollution case at Beijing on 12 January 2013 (haze day) as compared to those registered on 9 January (non-haze day). We study the evolution of the aerosol size distribution using retrievals from a ground-based CIMEL sun-sky radiometer of the Aerosol Robotic Network (AERONET). Our results show that while the hourly volume growth rate of a sub-micron fine mode presented in the size distribution remains below 0.010 µm3/µm2/hr during the non-haze day, it can rapidly increase during haze pollution event, reaching a maximum value of 0.075 µm3/µm2/hr. The mean size of fine mode particles becomes larger during the pollution event, while it is reduced for coarse mode particles. The mean volume of water uptake is 0.013 µm3/µm2 in haze day, being about 13 times larger than that in non-haze day. Meanwhile, the volume of water-soluble inorganic aerosols increases from 0.036 to 0.298 µm3/µm2, partly explained by the increase of water uptake during the haze event and also likely by accumulation of particle matters due to stagnating atmospheric conditions. The increase of water-soluble particle volume, which is enhanced by water uptake, significantly contributes to haze evolution.