A martensitic stainless steel provided includes C: 0.01-0.1% and Cr: 9-15%, and the retained austenite phase has a thickness not more than 100 nm in such a manner that the X-ray integral intensities of 111.gamma. and 110.alpha. satisfy the following formula (a): 0.005.ltoreq.111.gamma./(111.gamma.+110.alpha.).ltoreq.0.05 (a) Such a metal structure can be obtained by the following procedure: the steel is heated at a temperature of the Ac.sub.3 point or more, and then cooled from 800.degree. C. to 400.degree. C. at a cooling rate of not less than 0.08.degree. C./sec and further cooled down to 150.degree. C. at a cooling rate of not more than 1.degree. C./sec. The martensitic stainless steel according to the present invention has a relatively high carbon content and a greater toughness in spite of a high mechanical strength, and further exhibits an excellent corrosion resistance, so that it is particularly effective as the material for constructing a deep oil well.