Various morphologies of single-crystal Cu2O such as cube, octahedron, {110} truncated octahedron, and microrhombic dodecahedron with {110} surfaces are prepared in high yield through a facile solution-based one-step reduction method in an alkaline H2O/ethanol/oleic acid system in the presence of d-(+)-glucose. The formation mechanism of these microcrystals has been clarified as the synergic effect of oriented attachment and ripening mechanism.