The intermediate stage sintering kinetics of undoped ZnO and ZnO doped with 0.1-1.2 mol% Mn were investigated. It was found that the densification in the initial and intermediate stages is affected by surface diffusion in both undoped and Mn-doped ZnO, and that this contribution increases with the increase in the Mn content. The surface diffusion causes an initial pore growth, a more significant grain growth, and an apparent increase in the activation energy for densification at lower densities. Further kinetic analysis showed that the densification process in the intermediate stage is dominated by volume diffusion in all the compositions. The calculated values of the diffusion coefficients are consistent with the ones obtained by the tracer diffusion measurements of Zn in ZnO crystals in other works. The origin of the increase of the surface transport is discussed, together with its effect on the second phase mobility.