The epitaxial growth of GaN on patterned c-plane sapphire substrates having microlenses with a flat top, a dull tip, or a sharp tip is carried out. The growth mode, dislocation density, residual strain, and optical properties of GaN are investigated and correlated with the shape of the microlens. Because the growth of GaN does not take place on top of the microlens with a sharp tip, this type of patterned substrate leads to a wider low dislocation density lateral growth region, while it also gives rise to a higher compressive residual strain in GaN. For GaN grown on the microlens with a dull tip, many dislocations appear, resulting from the extra facets on the lens. It, however, has the lowest compressive strain among the samples studied. This work provides a guideline for preparing microlens patterned sapphire substrates for potential applications in high brightness InGaN light emitting diodes as both dislocation density and strain influence their internal quantum efficiency.