The road projects in Kenya have been experiencing poor performance in form of delays in completion, high cost, and low quality. This study objective was to assess the moderating effect of government regulations on the relationship between project planning and performance of completed road projects in arid and semi-arid counties in Kenya. The study was anchored on theory of constraints and supported by Stakeholder Theory, Resource Based View Theory and Regulation Theory. The study adopted positivism philosophy. The study applied a cross sectional survey design and used census sample method. The study population were the 88 completed road projects in 22 Arid and Semi-arid counties in Kenya. The study adopted convenience sampling technique where primary data was collected using a questionnaire from 198 respondents. The study respondents were the contracted company's project managers, county public works officers and the local community leaders who are most advantageously placed and in the best position to provide the information required. Quantitative data was analyzed using descriptive and inferential statistics which included correlation and multiple regressions. The research demonstrates a significant positive correlation (r = 0.477, p < 0.001) between government regulations and the performance of completed road projects in arid and semi-arid counties in Kenya. It highlights the critical influence of government regulations, including a regulatory framework and a code of conduct, on project outcomes in these regions. The study aimed to assess the moderating effect of government regulations on the relationship between project planning and performance, ultimately rejecting the null hypothesis of no moderation effect. Results confirm that government regulations significantly moderate this association, with project planning identified as a key predictor of project performance. This emphasizes the need for effective governance and regulatory measures to improve road project efficacy. Recommendations include strengthening and implementing comprehensive government regulations to guide project planning and execution. Additionally, training programs should be established for stakeholders to ensure understanding and adherence to these regulations. Regular assessments and updates of the regulatory framework are essential to address the unique challenges of arid environments. Collaboration between government agencies and local communities should be enhanced to incorporate community needs into project planning. Finally, investing in monitoring and evaluation systems will facilitate ongoing assessment of project performance and regulatory compliance, ultimately fostering successful road infrastructure development