Optical disk and optical information recording method

A rewritable phase change optical disk and a method of recording optical information on the optical disk in which a first dielectric film (2), a recording film (3), a second dielectric film (4) and a reflecting film (5) are stacked on a substrate (1) in this order; the recording film (3) having composition defined by a formula GexSbyTez wherein x, y and z are atomic percentages ranging from 7 to 17, 34 to 44 and 44 to 54, respectively, the x, y and z totalling 100; the recording film (3) having a thickness of 10 to 35 nm; the second dielectric film (4) having a thickness of 5 to 40 nm; the reflecting film (5) being made of one or an alloy of at least Au, Al, Ti, Cr and Ni and having a thickness of 35 nm or more.