ABSTRACT: Background:Despite the health system efforts, health disparities exist across sub-populations in India. We assessed the effects of health behaviour change interventions through women's self-help groups (SHGs) on maternal and newborn health (MNH) behaviours and socio-economic inequalities. Methods:We did a quasi-experimental study of a large-scale SHG program in Uttar Pradesh, India, where 120 geographic blocks received, and 83 blocks did not receive health intervention. Data comes from two cross-sectional surveys with 4,615 recently delivered women in 2015, and 4,250 women in 2017. The intervention included MNH discussions in SHG meetings and community outreach activities. The outcomes included antenatal, natal and postnatal care, contraceptive use, cord care, skin-to-skin care, and breastfeeding practices. Effects were assessed using multilevel mixed-effects regression adjusted difference-in-differences (DID) analysis adjusting for geographic clustering and potential covariates, for all, most-marginalised and least-marginalised women. Concentration indices examined the socio-economic inequality in health practices over time. Findings:The net improvements (5-11 percentage points [pp]) in correct MNH practices were significant in the intervention areas. The improvements over time were higher among the most-marginalised than least-marginalised for antenatal check-ups (DID: 20pp, p<0•001 versus DID: 6pp, p?=?0•093), consumption of iron folic acid tablets for 100 days (DID: 7pp, p?=?0•036 versus DID: -1pp, p?=?0•671), current use of contraception (DID: 12pp, p?=?0•046 versus DID: 10pp, p?=?0•021), cord care (DID: 12pp, p?=?0•051 versus DID: 7pp, p?=?0•210), and timely initiation of breastfeeding (DID: 29pp, p?=?0•001 versus DID: 1pp, p?=?0•933). Lorenz curves and concentration indices indicated reduction in rich-poor gap in health practices over time in the intervention areas. Interpretation:Disparities in MNH behaviours declined with the efforts by SHGs through behaviour change communication intervention.