ABSTRACT: OBJECTIVE:To determine whether Rojiroti microfinance, for poor Indian women, improves child nutrition. DESIGN:Cluster randomised trial. SETTING:Tolas (village communities) in Bihar State. PARTICIPANTS:Women and children under 5 years. INTERVENTIONS:With Rojiroti microfinance, women form self-help groups and save their money to provide loans to group members. After 6 months, they receive larger external loans. Tolas were randomised to receive Rojiroti immediately or after 18 months. OUTCOME MEASURES:The primary analysis compared the mean weight for height Z score (WHZ) of children under 5 years in the intervention versus control tolas who attended for weight and height measurement 18 months after randomisation. Secondary outcomes were weight for age Z score (WAZ), height for age Z score, mid-upper arm circumference (MUAC), wasting, underweight and stunting. RESULTS:We randomised 28 tolas to each arm and collected data from 2469 children (1560 mothers) at baseline and 2064 children (1326 mothers) at follow-up. WHZ was calculated for 1718 children at baseline and 1377 (674 intervention and 703 control) at follow-up. At 18 months, mean WHZ was significantly higher for intervention (-1.02) versus controls (-1.37; regression coefficient adjusted for clustering ?=0.38, 95%?CI 0.16 to 0.61, p=0.001). Significantly fewer children were wasted in the intervention group (122, 18%) versus control (200, 29%; OR=0.46, 95%?CI 0.28 to 0.74, p=0.002). Mean WAZ was better in the intervention group (-2.13 vs -2.37; ?=0.27, 95%?CI 0.11 to 0.43, p=0.001) as was MUAC (13.6?cm vs 13.4?cm; ?=0.22, 95%?CI 0.03 to 0.40, p=0.02). In an analysis adjusting for baseline nutritional measures (259 intervention children and 300 control), only WAZ and % underweight showed significant differences in favour of the intervention. CONCLUSION:In marginalised communities in rural India, child nutrition was better in those who received Rojiroti microfinance, compared with controls. TRIAL REGISTRATION NUMBER:NCT01845545.