Diffuse reflectance spectra of pure and diluted samples of nickel monoxide powder have been studied in the region 200–1000 nm. Three bands have been observed. The bands near 710, 450, and 227 nm have been assigned to 3A 2g → 3T 1g( 3F), 3A 2g → 3T 1g( 3P) , and electron transfer transitions, respectively.