In this study, we analyzed the elderly joint movements and changes in muscle length during STS at various sitting heights through the motion analysis and the musculoskeletal modeling. Five elderly and five young were participated in this experiment. Three heights of sitting posture which could represent typical sitting in Korean daily life were chosen as table seat (42cm), bath seat (21cm) and bottom (0cm). As the results, the elderly showed both smaller knee/hip flexion and larger trunk flexion relatively in comparison to the young during table seat STS. The elderly also showed larger dorsi flexion and smaller ROM of knee, hip, trunk compared to the young during bath seat STS. Additionally, the elderly showed larger plantarflexion, hip flexion, smaller knee flexion and trunk flexion during the first half of bottom STS and larger knee flexion, hip flexion and trunk flexion during the second half of bottom STS. In addition, we could know contraction and relaxation characters of major muscles in lower limb during various STS through the analysis of changes in muscle length by musculoskeltal modeling.