Objectives. To explore the dyadic interdependence of self-efficacy, benefit finding, anxiety, depression, and QOL in cancer patient (CP) and family caregiver (FC) dyads, and to ascertain the dyadic effects of self-efficacy on quality of life (QOL) in CP-FC dyads. Methods. Conducted from November 2014 to December 2015, participants comprised 772 CP-FC dyads. The study surveyed participant characteristics, self-efficacy, benefit finding, anxiety, depression, and QOL. Data were analyzed using Pearson’s correlation, T-test, and actor-partner interdependence mediation model (APIMeM). Results. CPs’ self-efficacy was positively correlated with both their own and FCs’ benefit finding and mental component summary (MCS), and negatively associated with anxiety and depression (all Ps < 0.01, |r| = 0.144∼0.432). However, CPs’ self-efficacy was only positively correlated with their own physical component summary (PCS) (r = 0.193), but not FCs’ PCS. The same profile was identified in FCs’ self-efficacy (all Ps < 0.01, |r| = 0.100∼0.468). FCs reported higher levels of self-efficacy and PCS compared to CPs (both Ps < 0.001). Significant positive correlations (r = 0.168–0.437) were identified among all paired variables in CP-FC dyads (all Ps < 0.001). To some extent, dyads’ self-efficacy influences dyads’ MCS and PCS through improving positive emotions (benefit finding) and relieving negative emotions (anxiety and depression). Conclusions. Study findings not only support the dyadic interdependence of self-efficacy, benefit finding, anxiety, depression, and QOL in CP-FC dyads but confirm the hypothesis that dyads’ self-efficacy may impact their MCS/PCS via an indirect approach to improve benefit finding and relieve anxiety and/or depression in CP-FC dyads.