The present invention aims to provide a polypropylene fiber (PP fiber) excellent in strength, heat resistance, and water-absorption properties, a method of producing the same, and a hydraulic composition, a rope, a sheet-shaped fiber structure, and a composite material with an organic polymer each using the PP fiber. The present invention provides: a PP fiber having a fiber strength of 7 cN/dtex or more and having either or both of (i) DSC properties such that the endothermic peak shape by DSC is a single shape having a half width of 10.degree. C. or lower and the melt enthalpy change (AH) is 125 J/g and (ii) irregular properties such that the single fiber fineness is 0.1 to 3 dtex and irregularities are formed on the surface, the irregularities having an average interval of 6.5 to 20 .mu.m and an average height of 0.35 to 1 .mu.m as a result of alternate presence of a protruded portion having a large diameter and a non-protruded portion having a small diameter along its fiber axis; a method of producing the PP fiber by pre-drawing an undrawn PP fiber having an IPF of 94% or more at 120 to 150.degree. C. at a drawing magnification of 3 to 10 times, and then post-drawing the resultant at 170 to 190.degree. C. and a drawing magnification of 1.2 to 3.0 times under the conditions of a deformation rate of 1.5 to 15 times/min and a draw tension of 1.0 to 2.5 cN/dtex; and a hydraulic composition, a rope, a sheet-shaped fiber structure, and a composite material with an organic polymer each using the PP fiber.