In Fredrickson’s positivity resonance theory, interacting people are connected via shared positive affect, mutual care, and biobehavioral synchrony. We tested the hypothesis that moments of shared positive affect are associated with greater physiological synchrony (i.e., responses are positively correlated or changing in the same direction). Couples in long-term marriages (n=156) had a 15-minute conflict conversation in the laboratory. Five physiological measures (e.g., heart rate) and facial behaviors were monitored continuously. Positive (and negative, as a comparison measure) affective behaviors of each partner for each second of the conversation were coded using the Specific Affect Coding System. For each physiological measure, we computed the time series of synchrony scores between the partners using a 15-second rolling window. Analyses focused on the average of these five time series synchrony scores. We found that moments (seconds) when both partners showed positive affect were associated with greater physiological synchrony. In contrast, moments when both partners showed negative affect were associated with lower physiological synchrony (in fact, their physiological responses were more negatively correlated, or changing in opposite directions). Findings support the hypothesis that moments of shared positive affect are characterized by physiological synchrony, suggesting a possible mechanism through which people connect during conflict.