Modified cellulose fibers, wherein each of (A) one or more substituents selected from substituents represented by the following general formula (1) and substituents represented by the following general formula (2): —CH2—CH(OH)—R1 (1); —CH2—CH(OH)—CH2—(OA)n-O—R1 (2), wherein each R1 in the general formula (1) and the general formula (2) is independently a linear or branched alkyl group having 3 or more carbon atoms and 30 or less carbon atoms; n in the general formula (2) is a number of 0 or more and 50 or less; and A is a linear or branched, divalent saturated hydrocarbon group having 1 or more carbon atoms and 6 or less carbon atoms, and (B) a substituent represented by the following general formula (3): —CH2—CH(OH)—R2 (3), wherein R2 in the general formula (3) is an alkyl group having 1 or more carbon atoms and 2 or less carbon atoms, is independently bonded to cellulose fibers via an ether bond, wherein the modified cellulose fibers have a cellulose I crystal structure. The resin composition blended with the modified cellulose fibers of the present invention can be suitably used in various industrial applications such as daily sundries, household electric appliance parts, wrapping materials for household electric appliance parts and automobile parts.