Purpose: The purpose of the study was to determines the effect of Internal Environment Management Practices on Supply Chain Performance among Agri-Manufacturing Firms in RwandaMethodology: This study employed both cross-sectional and explanatory research design and is in line with positivism approach. The target population was 567 top and middle employees in supply chain department from 67 Agri-Manufacturing Firms. Stratified and simple random sampling was used to select a sample of 226. This study collected both secondary and primary data, but mainly primary data using a structured questionnaire. Data analysis was performed with the aid of SPSS version 22.0 (Hayes and Matthes, 2009) using both descriptive and inferential statistics. Hypothesis 1 to 4 was tested using multiple regression model, while hypothesis 5 was tested using hierarchical regression.Results: Findings showed that internal environmental management positively and significantly influences supply chain performanceUnique contribution to Theory and Practice: It is therefore important for both the senior managers and mid – level managers to be committed and supportive of GSCM. Besides that, there is need for the firm to have total quality environmental management and ISO 14001 for environmental compliance. As well, having a team within the firm that is tasked with environmental improvements will go a long way in enhancing supply chain performance