Abstract: Taking aerosol field measurement experiments conducted in the summer of 2016 at Xingtai (XT) site and the 2016 and 2017 winters at Beijing (BJ) site as examples, the effects of typical new particle formation (NPF) events on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity were investigated. BJ and XT are respectively located in a northern megalopolis area and a central–southern industrial area in the North China Plain. The formation mechanisms of new particles in different seasons at the two sites were different, and the corresponding condensation sink, growth rate, and aerosol chemical composition were also different. Organics and sulfate were the dominant chemical species formed during NPF events at the BJ and XT sites, respectively. Furthermore, the XT site exhibited significantly stronger aerosol hygroscopicity and CCN activity than the BJ site, especially for the nucleation mode particles. The results of this study indicate that the difference in aerosol hygroscopicity and activation ability should be fully considered in the estimation of the influence of NPF on CCN number concentration.