A rear fender supporting structure of a saddle-type vehicle comprising: a rear wheel which is supported through a swing arm to a body frame swingably in an upper-lower direction; and a rear fender which covers a rear upper part of the rear wheel, wherein the rear fender is supported to the swing arm on one side in a left-right direction of the saddle-type vehicle, wherein the swing arm includes: an arm portion which extends in a front-rear direction of the saddle-type vehicle; a through hole which is provided at a rear end of the arm portion to support an axle; and a split-clamp portion which supports the axle by fastening an upper circular-arc and a lower circular-arc surrounding the through hole with a fastening member, and wherein the rear fender is mounted on a front-side fixing portion which is positioned on a front side of the upper circular-arc and is on an upper surface of the arm portion, and on a rear-side fixing portion which is positioned on a rear side of the lower circular-arc, wherein the swing arm has a cantilever structure configured only by a side on which a power transmission member for the rear wheel is provided in the left-right direction of the saddle-type vehicle, wherein the split-clamp portion has a structure in which the upper circular-arc and the lower circular-arc fasten an outer circumference of a circular cam member capable of adjusting a position of the axle with respect to the swing arm, and characterized in that the front-side fixing portion and the rear-side fixing portion are disposed substantially on a diagonal line with the circular cam member interposed therebetween. a rear wheel which is supported through a swing arm to a body frame swingably in an upper-lower direction; and a rear fender which covers a rear upper part of the rear wheel, wherein the rear fender is supported to the swing arm on one side in a left-right direction of the saddle-type vehicle, wherein the swing arm includes: an arm portion which extends in a front-rear direction of the saddle-type vehicle; a through hole which is provided at a rear end of the arm portion to support an axle; and a split-clamp portion which supports the axle by fastening an upper circular-arc and a lower circular-arc surrounding the through hole with a fastening member, and wherein the rear fender is mounted on a front-side fixing portion which is positioned on a front side of the upper circular-arc and is on an upper surface of the arm portion, and on a rear-side fixing portion which is positioned on a rear side of the lower circular-arc, an arm portion which extends in a front-rear direction of the saddle-type vehicle; a through hole which is provided at a rear end of the arm portion to support an axle; and a split-clamp portion which supports the axle by fastening an upper circular-arc and a lower circular-arc surrounding the through hole with a fastening member, and wherein the rear fender is mounted on a front-side fixing portion which is positioned on a front side of the upper circular-arc and is on an upper surface of the arm portion, and on a rear-side fixing portion which is positioned on a rear side of the lower circular-arc, wherein the swing arm has a cantilever structure configured only by a side on which a power transmission member for the rear wheel is provided in the left-right direction of the saddle-type vehicle, wherein the split-clamp portion has a structure in which the upper circular-arc and the lower circular-arc fasten an outer circumference of a circular cam member capable of adjusting a position of the axle with respect to the swing arm, and characterized in that the front-side fixing portion and the rear-side fixing portion are disposed substantially on a diagonal line with the circular cam member interposed therebetween.