Purpose The purpose of this case study was to compare immediate changes in spatiotemporal gait variables and subjective responses after applying a 3Dprinted customized MediACE3D insole and a FEET PRINT 5.0 EXPERT thermoformed customized insole (FP5.0ETCI) in patients with degenerative knee osteoarthritis. Methods Three patients with degenerative knee osteoarthritis who were able to walk independently participated in this singlegroup repeatedmeasures case study. Gait analysis was performed under three conditions: no insole (NI), 3Dprinted customized insole (3DPCI), and FP5.0ETCI. Gait measurements were conducted under the same shoe condition using a zebris gait analysis system. Each condition was measured three times, and the mean value of stable trials was used for analysis. Results Compared with the NI condition, stride length and cadence increased in all participants after wearing both customized insoles. Calculated stride time decreased and calculated velocity increased in both insole conditions. The 3DPCI condition showed relatively greater increases in stride length and velocity, whereas the FP5.0ETCI condition showed higher subjective scores for insole fit, walking stability, and overall satisfaction. Conclusion Both customized insoles produced favorable immediate changes in spatiotemporal gait variables compared with the NI condition. The 3DPCI may have advantages in changing objective gait variables, whereas the FP5.0ETCI may have advantages in comfort and perceived walking stability. Because this study included only three cases, the findings should be interpreted as preliminary observations, and further studies with larger samples and additional plantar pressure and kinetic variables are needed.