Pure ZnO thin films were spin coated on glass substrates using 0.5M Zinc acetate dihydrate precursor solution and then annealed at 500°C for 2h in air to get good quality thin films. The effect of sol-aging time, from as-synthesized to 4week aged, on microstructure and morphology of ZnO thin films was investigated. X-ray diffraction spectra revealed the polycrystalline wurtzite structure preferentially oriented along the (002) polar plane with variable peak intensity. AFM analysis exposed an asymmetrical cyclic morphology transition with sol-aging time from comparatively smooth surfaces with small spherical particles to a rigid wrinkle network of a high rms surface roughness value of at～42.4nm which finally untied and evolved as homogeneous surface of uniform grain distribution after 4 weeks of aging time. The minimum surface roughness of 1.6nm was obtained for the film prepared from 24h aged solution.