The authors are conducting a series of studies in order to design stumbling-resistant socks for elderly people. In this report, we studied (1) the relationship between walking ability test scores and gait dynamics and (2) the effects of design factors of the socks, specifically the insole and upper shoe areas, on gait dynamics. The subjects consisted of eleven elderly females. As previously reported, we used the difference between the maximum and the minimum values (ΔS) in the angular velocities of the hip, knee, and ankle joints as an index to evaluate stumbling resistance. We conducted a principal component analysis using the scores from the walking ability test, with the total walking power as the first main component and wobble as the second main component. Subjects with decreased total walking power had a decreased ΔS of the angular velocities of the hip and knee joints. Subjects with increased wobble had a decreased ΔS of the angular velocities of the ankle joint. Several sock designs were tested, however, when subjects were wearing socks with a medial-longitudinal arch in the insole and supporting function on the sides of the foot (sample O), they had increased ΔS of the angular velocity in all joints. In conclusion, it was found that the sample O sock was effective for stumbling resistance. This effect was more prominent in subjects with gait difficulties, i.e., decreased walking power and increased wobble.