Africa has been experiencing rapid urbanization, yet limited studies have systematically investigated urban growth dynamics across African cities. Using 25 cities as cases, we quantified urban growth and form changes in Africa via spatiotemporal analysis of urban land densities in concentric rings over three time points (1990, 2000, and 2014). The results show that African cities have rapidly grown both in population and built-up areas, which increased by about 4% and more than 5% per annum, respectively. Urban land density (defined as the proportion of the built-up area to the buildable area) in each concentric ring decreases from the city center to the urban periphery with diverse patterns among cities. Comparatively, small cities have a lower urban land density and a more dispersed urban form than medium-sized and large cities in Africa. The international comparisons between cities with over one million population in Africa, Asia (e.g., China and India), Europe, and North America (i.e., the United States) reveal that African cities have a relatively less compact urban form. Implications of these findings for the future of African cities are further proffered.