The present invention relates to a low-alloy steel, seamless steel pipe for oil well, and process for producing seamless steel pipe. A low-alloy steel is characterized by containing, in terms of mass%, 0.10-0.20% C, 0.05-1.0% Si, 0.05-1.5% Mn, 1.0-2.0% Cr, 0.05-2.0% Mo, up to 0.10% Al, and 0.002-0.05% Ti and having a value of Ceq calculated with the following equation (1) of 0.65 or higher, the remainder being iron and impurities. It is further characterized in that the impurities include up to 0.025% P, up to 0.010% S, up to 0.007% N, and less than 0.0003% B and that the number of M23C6 precipitate (M is a metal element) particles having a particle diameter of 1 [mu]m or larger is 0.1 or smaller per mm. The low-alloy steel retains suitability for quenching and toughness and improves resistance to sulfide stress corrosion cracking. Ceq = C + (Mn/6) + (Cr+Mo+V)/5 (1) In the equation (1), C, Mn, Cr, Mo, and V indicate the proportions in mass% of the respective elements.