<p>Using a multistep nitrite-coated filter-pack system for sampling, we determined the seasonal variations in the triple oxygen isotopic composition (<em>Δ</em><sup>17</sup>O) of tropospheric ozone (O<sub>3</sub>) in the terminal positions (<em>Δ</em><sup>17</sup>O<sub>term</sub>(O<sub>3</sub>)) in the cities Nagoya and Niigata (Japan) in the eastern Asia region to quantify the mixing ratio of stratospheric O<sub>3</sub> within the total tropospheric O<sub>3</sub> supplied by stratosphere–troposphere transport (STT). In Nagoya, diurnal variations have also been studied. Both the average <em>Δ</em><sup>17</sup>O<sub>term</sub>(O<sub>3</sub>) and their 1σ variation ranges agreed well with previous studies, (37.5 ± 1.4) ‰ in Nagoya and (37.0 ± 1.7) ‰ in Niigata. The average difference in <em>Δ</em><sup>17</sup>O<sub>term</sub>(O<sub>3</sub>) between daytime (higher) and nighttime (lower) was (1.4 ± 0.7) ‰ (1σ) in Nagoya, which was responsible for the formation of a stable boundary layer at night, reducing mixing with high <em>Δ</em><sup>17</sup>O<sub>term</sub>(O<sub>3</sub>) from the free troposphere. We also found a significant correlation between <sup>7</sup>Be activity concentrations and the <em>Δ</em><sup>17</sup>O<sub>term</sub>(O<sub>3</sub>), implying that STT was responsible for the elevated <em>Δ</em><sup>17</sup>O<sub>term</sub> of O<sub>3</sub> in the troposphere. By using the relationship between the reciprocal of concentrations and <em>Δ</em><sup>17</sup>O<sub>term</sub> of tropospheric O<sub>3</sub>, we estimated the <em>Δ</em><sup>17</sup>O of stratospheric O<sub>3</sub> supplied through the STT (<em>Δ</em><sup>17</sup>O<sub>STT</sub>), together with that produced through photochemical reactions at surface altitude (<em>Δ</em><sup>17</sup>O<sub>sur</sub>). Moreover, using <em>Δ</em><sup>17</sup>O<sub>STT</sub> and <em>Δ</em><sup>17</sup>O<sub>sur</sub>, we estimated the mixing ratios of stratospheric O<sub>3</sub> (i.e., O<sub>3</sub> produced in the stratosphere and supplied to the troposphere through STT) in each tropospheric O<sub>3</sub> (<em>f</em><sub>STT</sub>), as well as the absolute concentrations of stratospheric O<sub>3</sub> supplied through STT in the troposphere (<em>C</em><sub>STT</sub>(O<sub>3</sub>)). The <em>C</em><sub>STT</sub>(O<sub>3</sub>) exhibited minimum values in summer ((5.3 ± 1.0) ppb) and maximum values in late winter to spring ((15.9 ± 2.1) ppb). Although the <em>f</em><sub>STT</sub> values were higher than those estimated using the chemistry climate models from past studies, the trends of the seasonal variations were consistent with them. We concluded that <em>Δ</em><sup>17</sup>O successfully provided observational constraints on the STT of O<sub>3</sub>.</p>