AA 1050 aluminum lithographic plates were ac electrograined in nitric acid electrolyte using a flow cell. Scanning electron microscopy was employed to characterize the surface morphology of the electrograined aluminum plate. An epoxy replica technique was utilized to reveal the internal structures of the etch pits. Cross-sectional transmission electron microscopy was employed for revealing the detailed morphology of the etch pits and the microstructure of the etch film. Together with the surface property measurements such as R-a, R-max, peak count, and relative increase factor, a pit nucleation and growth sequence is discussed. Numerous hemispherical pits nucleated and grew on the original aluminum surface upon ac electrograining. One-dimensional and two-dimensional coalescence of the individual hemispherical pits led to the formation of crescent-shaped and convoluted pits, respectively. Secondary stage of pit nucleation and growth occurred dominantly on the walls of the convoluted pits. Formation of convoluted pits on the walls of the existing convoluted pits resulted in a pronounced increase in R-a and R-max. Meanwhile, a decrease in peak count and relative increase factor was observed for prolonged electrograining. In addition, the microstructure of the etch film was closely related to the morphology of the etch pits.