Nanocrystalline Cu2O thin films have been synthesized using an activated reactive evaporation technique. Structural and optical characterizations of these films have been carried out using: glancing angle X-ray diffractometer; Fourier transform infrared spectrometer; transmission electron microscope; and LTV-VIS-NIR spectrophotometer. The nanocrystallite size in these films was varied by varying deposition parameters. Optical studies show a direct allowed transition and a shift in the optical absorption edge from the bulk value with nanocrystallite size and stoichiometry of these films. These results show that single phase nanocrystalline Cu2O thin films can be synthesized at a relatively low substrate temperature using the activated reactive evaporation technique. These studies indicate that nanocrystallinity results in the stability of cubic Cu2O phase in these films.