【Purpose】Sauna bathing has been reported to be associated with reduced cardiovascular mortality. Conversely, it has been suggested that cold-water bathing may negatively affect the cardiovascular system, such as by acutely increasing systolic blood pressure. This study investigated the effects of alternating contrast bathing, a fusion of sauna and cold-water bathing, on the cardiovascular system, employing arterial stiffness as a key index.  【Method】The participants included 11 healthy young men (21.3±0.6 years) who were divided into the sauna bathing group (10 min of sauna bathing, 1 min of showering, 5 min of rest; 3 sets) or the contrast bathing group (10 min of sauna bathing, 1 min of cold-water bathing, 5 min of rest; 3 sets). A cross-over test was conducted. To eliminate dehydration effects, each participant ingested 500 mL of water from immediately before through during the bathing protocol. Arterial stiffness, an index of the cardiovascular system, was evaluated using brachial-ankle pulse wave velocity (baPWV). BaPWV was measured pre-bathing, immediately after bathing, and 30 min after bathing. The bathing temperature settings were 86°C for the sauna, 40°C for the shower, and 17°C for the cold bath. Statistical analysis was performed using a two-way analysis of variance (ANOVA) with bathing method (contrast bath, sauna) and time (before bathing, immediately after bathing, 30 min after bathing) as factors.  【Result】Two-factor analysis of variance on bathing method and time course in relation to baPWV results revealed no interaction between bathing method and time course. However, a main effect was observed in the factor of time course (p＝0.038), and a significant decrease was observed at 30 min after bathing compared with pre-bathing (p＝0.034).  【Conclusion】In healthy young men hydrated with 500 mL of fluid, both sauna bathing and contrast bathing significantly reduced arterial stiffness, with no significant difference between them. Future research should assess these effects in diverse populations, accounting for bathing protocols and participants’ age and health.