Walking ability is positively related to the quality of life of elderly persons. As a walking assistive device, one of the major goals should be to improve walking performance after repeating use of the device. Toward this goal, this paper experimentally evaluates the long-term effect of an authors' soft robotic suit, which has been developed to assist hip flexion for elderly persons in daily activities, on gait improvement in a 80-years-old healthy female subject. Experimental results show that the effects of the robotic suit are twofold. One is the immediate effect of improving lower limb cooperation by the hip flexion assistance. That is, walk ratio of the subject increased at most 14.9 % in the condition of the robotic suit worn and powered on (PON) compared with the condition of robotic suit worn but powered off (POFF). The other one is the long-term effect of increasing motion range of lower limb by rehabilitation training. Namely, as a residual result of the immediate effect, walk ratio in the POFF condition increased 28.6 % after 6-week repeating use of the robotic suit. The results of this study are useful for the development of a training program for the effective use of the robotic suit in gait rehabilitation, and the future development of soft walking assistive devices for gait rehabilitation of elderly persons.