An oil pump rotor for use in an oil pump includes an inner rotor having (n: “n” is a natural number) external teeth, an outer rotor having (n+1) internal teeth meshing with the external teeth, and a casing forming a suction port for drawing a fluid and a discharge port for discharging the fluid, such that in association with meshing and co-rotation of the inner and outer rotors, the fluid is drawn/discharged to be conveyed according to volume changes of cells formed between teeth faces of the two rotors. For a tooth profile formed of a mathematical curve and having a tooth addendum circle A1 with a radius RA1 and a tooth root curve A2 with a radius RA2, a circle D1 has a radius RD1 which satisfies Formula (1) and a circle D2 has a radius RD2 which satisfies both Formula (2) and Formula (3), RA1>RD1>RA2  Formula (1) RA1>RD2>RA2  Formula (2) RD1≧RD2  Formula (3) a tooth profile of the external teeth of the inner rotor includes at least either one of a modification, in a radially outer direction, of the tooth profile, on the outer side of the circle D1 and a modification, in a radially inner direction, of the tooth profile, on the inner side of the circle D2.