Excellent resistance to sulfide stress cracking resistance OCTG

Having excellent SSC-resistance of OCTG. OCTG of the present invention provides that by mass%, C: 0.15 ~ 0.35%, Si: 0.1 ~ 0.75%, Mn: 0.1 ~ 1.0%, Cr: 0.1 ~ 1.7%, Mo: 0.1 ~ 1.2%, Ti : 0.01 ~ 0.05%, Nb: 0.010 ~ 0.030%, and Al: 0.01 ~ 0.1%, P: 0.03% or less, S: 0.01% or less, N: 0.007% or less, and O: 0.01% or less, and the balance Fe and impurities, by-bromo - Ti content and Nb content satisfies the formula (1) of the methanol extract obtained in the residue. 100 × [Nb] / ([Ti] + [Nb]) ≤27.5 (1), in this case, the [Ti], [of Nb] substituting the Ti content of the residue (mass%), of Nb content (mass%) .