BACKGROUND: Disparities in the use of maternal, neonatal and child health (MNCH) services remain a concern in Low- and Middle-Income countries such as Nepal. Commonly observed disparities exist in education, income, ethnic groups, administrative regions and province-level in Nepal. In order to improve equitable outcomes for MNCH and to scale-up quality services, an Investment Case (IC) approach was lunched in the Asia Pacific region. The study assessed the impact of the IC intervention package in maternal and child health outcomes in Nepal. METHODS: The study used a quasi-experimental design extracting data from the Nepal Demographic Health Surveys - 2011 (pre-assessment) and 2016 (post-assessment) for 16 intervention and 24 control districts. A Difference in Difference (DiD) analysis was conducted to assess the impact of the intervention on maternal and child health outcomes. The linear regression method was used to calculate the DiD, adjusting for potential covariates. The final models were arrived by stepwise backward method including the confounding variables significant at p < 0.05. RESULTS: The results of the DiD analyses showed at least four antenatal care visits (ANC) decreased in the intervention area (DiD% = - 4.8), while the delivery conducted by skilled birth attendants increased (DiD% = 6.6) compared to control area. However, the adjusted regression coefficient showed that these differences were not significant, indicating a null effect of the intervention. Regarding the child health outcomes, children with underweight (DiD% = 6.3), and wasting (DiD% = 5.4) increased, and stunting (DiD% = - 6.3) decreased in the intervention area compared to control area. The adjusted regression coefficient showed that the difference was significant only for wasting (β = 0.019, p = 0.002), indicating the prevalence of wasting increased in the intervention group compared to the control group. CONCLUSION: The IC approach implemented in Nepal did not show improvements in maternal and child health outcomes compared to control districts. The use of the IC approach to improve MCH in Nepal should be discussed and, if further used, the process of implementation should be strictly monitored and evaluated.