The effect of particle size on the UV absorption of zinc oxide nanoparticles has been investigated in the size range above the quantum limit. The results show that the absorbance increases with increasing size for particle sizes of 15–40 nm. The results are evaluated in terms of intrinsic particle absorption and the number concentration of particles. It is shown that the particles become opaque for particle sizes greater than 70 nm. For larger sizes the absorbance decreases with increasing size due to the decrease in particle concentration.