Purpose: Although it has been proposed that 1 spouse's health behaviors might correlate with the other spouse's health behavior among married couples, few studies have focused on sedentary behavior. This study examined whether objectively measured sedentary behavior and physical activity are correlated with each other and whether attachment to one's spouse moderates such correlations among middle-aged and older married couples. Methods: Seventy-two couples participated in the survey. This study measured time engaged in sedentary behavior and moderate-to-vigorous physical activity (MVPA), step counts by an accelerometer for 7 days, and attachment to one's spouse, age, education, and frailty by questionnaires. Results: Multiple regression analyses showed that the sedentary behaviors of 1 spouse statistically significantly regressed on those of the other spouse (ß = 0.30-0.47). The regressions of husbands' MVPA and step counts on those of their wives were statistically marginally significant (ß = 0.22-0.25), while the regressions of wives' MVPA and step counts on those of their husbands were not statistically significant (ß = 0.15-0.18). The interaction terms of the attachment with one's spousal accelerometer variables on those of the other spouse were not statistically significant (ß = -0.02 to 0.16). Conclusions: This study revealed that sedentary behaviors were correlated with each other among couples and attachment to one's spouse did not moderate these correlations. Sedentary behaviors of 1 spouse might influence the other, regardless of attachment to one's spouse. The concordance for physical activity was weaker than that for sedentary behavior.