(1) A nickel-base alloy product having, on the surface thereof, an oxide film comprising at least two layers, namely a first layer mainly composed of Cr2O3 and having a chromium content of not less than 50% relative to the total amount of metal elements and a second layer occurring outside the first layer and mainly composed of MnCr2O4, wherein the grain size of Cr2O3 crystals in the first layer is 50 to 1,000 nm and the total oxide film thickness is 180 to 1,500 nm. (2) A method of producing the nickel-base alloy product as specified above under (1) which comprises subjecting a nickel-base alloy product to oxide film formation treatment by maintaining the same at a temperature of 650 to 1,200° C. in a hydrogen atmosphere or hydrogen-argon mixed atmosphere showing a dew point of −60° C. to +20° C. for 1 to 1,200 minutes. The product mentioned above (1) allows only a very low level of Ni release in a high-temperature water environment over a long period of time and is particularly suited for use as a nuclear reactor member.