Introduction: This is a one-year post-intervention study following an initiative to provide orientation to female community health volunteers (FCHVs) on postpartum family planning in Nepal. In light of positive results in the earlier post-intervention study, this study was designed to provide a more long-term perspective on sustainability by assessing the effect at one-year post-intervention., Methods: This mixed-methods study was conducted in January 2020 in Morang district, Nepal. We collected quantitative data from a knowledge assessment of FCHVs who had participated in the intervention on postpartum family planning, data on their community-based counseling coverage and through interviews with postpartum mothers in two selected hospitals. Qualitative data were collected through six key informant interviews with health providers and four focus group discussions with FCHVs involved in the intervention. We performed descriptive and multivariate analyses for quantitative data and thematic analysis for qualitative data., Results: In total, 206 FCHVs participated in the one-year post-intervention study with significant improvement in knowledge of postpartum family planning as compared to pre-intervention period. The adjusted odds ratios (AOR) for knowledge of the 5 key messages on postpartum family planning as compared to the pre-intervention period included 1) knowledge on postpartum family planning can be used immediately after birth (AOR = 18.1, P<0.001), 2) postpartum intra-uterine device (PPIUD) can provide protection up to 12 years (AOR = 2.9, P = 0.011), 3) mothers who undergo cesarean section can use PPIUD (AOR = 2.3, P<0.001), 4) PPIUD can be inserted immediately after birth (AOR = 6.2, P <0.001), and 5) women should go for follow-up immediately if the IUD strings are seen outside vulva (AOR = 2.0, P = 0.08). The FCHVs answering 4 or more questions correctly was 10 times higher (AOR = 10.1, P<0.001) at one-year post-intervention, whereas it was 25 times higher at immediate-post-test (AOR = 25.1, p<0.001) as compared to pre-intervention phase. The FCHVs had counseled 71% of the pregnant women (n = 538) within their communities at one-year post-intervention. The postpartum mothers in hospitals had a 2 times higher odds of being counseled by FCHVs during their pregnancy at one-year post-intervention (AOR = 1.8, P = 0.039) than in pre-intervention phase. The qualitative findings suggested a positive impression regarding the FCHV's involvement in postpartum family planning counseling in the communities, however, supervision and monitoring over a longer term was identified as a key challenge and that may influence sustainability of community-based and hospital-based postpartum family planning services., Conclusion: The FCHVs' knowledge and community-based activities on postpartum family planning remained higher than in the pre-intervention. However, it declined when compared to the immediate post-intervention period. We propose regular supervision and monitoring of the work of the FCHVs to sustain progress., Competing Interests: No authors have competing interests.