The present invention relates to a multi-mode optical fiber having a structure enabling stable production and broadening of communication bandwidth as compared with the conventional structures. The multi-mode optical fiber has a core with a diameter 2a that is doped with GeO2 and chlorine. The chlorine concentration profile in the core along the diametric direction of the multi-mode optical fiber has a shape such that the chlorine concentration at a second measurement position within a range at a distance of from 0.9 a to 1.0 a from the center of the core in the radial direction thereof is higher than the chlorine concentration at a first measurement position at a distance of a/2 from the center of the core in the radial direction thereof.