The present invention aims to provide a process for producing cellulose nanofibers using a 4-hydroxy TEMPO derivative less expensive than TEMPO and a process capable of rapidly producing homogeneous cellulose nanofibers. Wood cellulose can be efficiently converted into nanofibers by a process for producing cellulose nanofibers comprising treating a cellulosic material with an oxidizing agent in water in the presence of a cellulose oxidation catalyst comprising an N-oxyl compound represented by formula 1 below:wherein R1 and R2 are each independently hydrogen or a C1-C6 straight or branched alkyl group; and(i) one of R4 or R5 is —OR, —OCOR or —OSO2R wherein R is a straight or branched carbon chain having 4 or less carbon atoms, and the other of R4 or R5 is hydrogen, and R3 and R6 are methyl, or(ii) R4 is hydrogen, and R5, R3 and R6 are taken together with a piperidine ring to form an aza-adamantane compound having formula 2 below:or a mixture thereof, and a compound selected from the group consisting of bromides, iodides and mixtures thereof to prepare oxidized cellulose, and microfibrillating the oxidized cellulose to convert it into nanofibers.