OBJECTIVE Serial follow-up data of body composition from peritoneal dialysis (PD) initiation until 1 year after kidney transplantation (KT) would be useful in identifying pathologic or physiologic changes, related to each modality or during the exchange of the modality. METHODS Body composition analysis was performed 1 month after PD initiation, repeated annually, immediately before KT, 1 month and 1 year after KT (n = 43). Body composition analysis was performed using a bioimpedance analysis (BIA) machine. The body composition parameters measured using BIA included the water contents, fat mass index (FMI), appendicular muscle mass index (aMMI), and bone mineral content (BMC). RESULTS The aMMI values 1 month and 1 year after PD initiation, immediately before KT, and 1 month and 1 year after KT were 7.6 ± 1.5, 7.8 ± 1.4, 8.0 ± 1.4, 6.8 ± 0.9, and 7.0 ± 1.0 kg/m2, respectively. The aMMI increased during the first year of PD (P = 0.029) and was maintained during the remaining period of PD (P = 0.413). The value decreased during the first month after KT (P < 0.001) and recovered during the first year after KT (P = 0.010). FMI increased during the first year of PD (P < 0.001) and was maintained during the remaining period of PD (P = 0.214). The value increased during the first year of KT (P < 0.001). BMC was stable during the PD period but decreased after KT. Body waters were maintained during PD and decreased after KT. The presence of low muscle mass (LMM) 1 month after PD initiation or 1 month after KT, was associated with development of LMM 1 year after KT. CONCLUSIONS Our study showed that body composition was significantly changed during the first year after PD or the first month after KT, as evidenced by a decrease in aMMI and BMC and an increase in FMI. Adequate interventions provided at these two points might help maintain proper body composition.