Disclosed are a steel sheet for a line pipe and a steel pipe for a line pipe, which have excellent low-temperature toughness and are most suitable for a steel pipe that is used for a line pipe for transportation of petroleum oil, natural gas or the like. The steel sheet for a line pipe and the steel pipe for a line pipe respectively contain, in mass%, 0.02-0.08% of C, 0.01-0.5% of Si, 1.2-1.8% of Mn, 0.001-0.10% of Nb, 0.0010-0.0050% of N, and 0.0001-0.0050% of Ca, while suppressing P to 0.01% or less, S to 0.0020% or less, Ti to 0.001-0.030%, Al to 0.030% or less and O to 0.0035% or less with the balance made up of Fe and unavoidable impurities. The steel sheet for a line pipe and the steel pipe for a line pipe satisfy the relation of S/Ca < 0.5, and have a maximum Mn segregation degree of 2.0 or less, an Nb segregation degree of of 4.0 or less and a Ti segregation degree of 4.0 or less.