A seamless steel pipe having a specific chemical composition. A ratio of Ti to N is in a range of 2.0 to 5.0. The steel pipe has a microstructure including tempered martensite having a volume ratio of 95% or more, and prior austenite grains having a grain size number of 8.5 or more. In a cross-section perpendicular to a rolling direction of the steel pipe a number of nitride-based inclusions having a particle size of 4 μm or more is 100 or less per 100 mm2, a number of nitride-based inclusions having a particle size of less than 4 μm is 1000 or less per 100 mm2, a number of oxide-based inclusions having a particle size of 4 μm or more is 40 or less per 100 mm2, and a number of oxide-based inclusions having a particle size of less than 4 μm is 400 or less per 100 mm2.