[Purpose] To investigate the effect of night splints on the standing motor function and ankle dorsiflexion angles of patients with Duchenne muscular dystrophy (DMD). [Subjects and Methods] Nine boys (age <11 years) with DMD were divided into the sufficiently-wearing group and the insufficiently-wearing group, according to how often they wore their splint for one year. We evaluated the changes between the pre-implementation and the one-year-after assessments of both the sufficiently-wearing group and the insufficiently-wearing group for the ankle dorsiflexion angle, North Star Ambulatory Assessment, 10-m running time, and time to stand from the floor. [Results] Only the left dorsiflexion angle of the ankle showed significantly difference for the sufficiently-wearing group. For other indicators, there were tendency toward improvement and maintenance in the sufficiently-wearing group. [Conclusion] The standing motor function improved significantly in some patients in the sufficiently-wearing group, suggesting that wearing night splints may promote the improvement and/or maintain of standing motor function in patients with DMD.