We have conducted radiocarbon (14C) dating of Japanese tree rings from 1053 to 921 BCE and 41 BCE to 130 CE. Dating was also performed using oxygen isotope dendrochronology to investigate subtle structures of the calibration curve corresponding to the beginning and the end of the Yayoi period in Japan. These two results followed IntCal20, which included the 14C ages of two Japan-sourced trees. The findings suggest that dating of specimens obtained from areas around the Japanese archipelago may be affected by periodic monsoons from the ocean, an effect that needs further examination.