The effects of the nanocrystal size on the emission spectra and decay rates of upconverting hexagonal NaYF(4):Yb,Er nanocrystals are investigated. The influence of nanocrystal size is represented in terms of the surface area/volume ratio (SA/Vol). Our results show that a small nanocrystal size, or large SA/Vol ratio increases the decay rate, in particular, the green luminescence decay rate varies linearly with the SA/Vol ratio.