Health mothers' groups are the nearest platform for women to access health information in Nepal. HMG functionality and factors affecting HMG participation in Nepal were explored. Background Nepal's female community health volunteers (FCHVs) each lead a monthly health mothers' group (HMG) to share health-related information and engage communities in the health system. Suaahara II (SII), a US Agency for International Development-funded multisectoral nutrition program, uses social and behavior change interventions to promote HMG participation and uses its health systems interventions to strengthen HMG quality. Objectives This study aimed to explore HMG functionality and variation across Nepal, including barriers and facilitators to attending HMG meetings. Methods SII's cross-sectional annual survey data from 16 districts (n = 192 FCHVs and 1850 mothers with children <2 y) were used. Descriptive and logistic regression analyses were conducted where the outcome variable was whether mothers were active HMG members or not, with FCHV and maternal characteristics as explanatory variables. Qualitative data were obtained from 3 of 16 survey districts (n = 30 observations, n = 30 in-depth interviews with mothers, and n = 16 focus group discussions with mothers, family members, FCHVs, health workers, and SII staff). Results Among FCHVs, 90% reported facilitating HMG meetings, whereas 64% of mothers reported HMG availability, and only 25% reported participating actively in meetings. Household head sex, maternal age, maternal education, maternal self-efficacy, and engagement with an FCHV and SII were associated with whether mothers were active participants in HMG meetings. Qualitative findings highlighted systems-level barriers, including lack of FCHV skills, demotivation, and heavy workload. Mothers noted time as the major constraint and family support, the HMG's savings component, and active FCHVs as facilitators to participation. Conclusions Findings suggest that both supply- and demand-side solutions are needed to improve HMG performance and uptake in Nepal. These solutions need to include improving FCHV skills and motivating them to provide high-quality HMG services, as well as encouraging family members to support women so that they have time to participate in the HMGs.