PROBLEM TO BE SOLVED: To provide a fumaric acid-containing fiber containing fumaric acid.SOLUTION: A fumaric acid-containing fiber has a substrate fiber and fumaric acid, where the substrate fiber contains a water absorptive fiber, the fumaric acid is added by removing water after contacting the water absorptive fiber and a fumaric acid-containing solution, the addition amount of the fumaric acid is in a range of 0.0001 to 0.15 pt.mass based on 100 pts.mass of the water absorptive fiber and a trend of heat release amount by bacterial growth shows that the bacterial growth can be suppressed.SELECTED DRAWING: Figure 1