Participation is a process through which stakeholders’ input and share control over development initiatives, decisions and resources which affect them. The concept of public participation in the budgeting process has been extensively examined by scholars. Various scholars are all in agreement that participation of stakeholders in the budgeting process adds value. This study sought to establish the effect of public participation on the budget preparation process in Kenya: a case of Mombasa county government. The specific objectives of the study were to establish the effect of public participation on budgetary allocation in Mombasa County, to determine the impact of public participation on budgetary implementation in Mombasa County, to determine how public participation enhances budgetary monitoring in Mombasa County and to determine the impact of public participation on budgetary review in Mombasa County. The study adopted a descriptive research design since the study intended to gather quantitative and qualitative data that would describe the effect of public participation on the budget preparation process in Mombasa County. The target population composed of employees of Mombasa County Government. This included both the employees on permanent and temporary contract employment which is 3800 employees. The study sampled 570 employees who were drawn from all cadres of staff. The study collected both primary and secondary data. Descriptive statistics were used to summarize the data. This included percentages and frequencies; tables and other graphical presentations were used for ease of understanding and analysis. The study conducted Pearson Correlation Analysis to predict the relationship between public participation and budget preparation process in Mombasa County.  The study findings revealed that enhanced citizen participation promoted budgetary allocation in Mombasa County and that well-planned citizen involvement programs related the expectations of the citizens and the planner. There  exists a positive relationship between public involvement in budgetary monitoring process and quality in budget preparation process, monitoring data derived from public involvement processes provided a critical perspective for making decisions in planning, budgeting, and management and that public involvement in budgetary implementation process allowed for adequate recording of appropriations, revisions in appropriations, transfers between appropriations, apportionment, and that community involvement is as a critical element of reputable governance. The study concluded that public involvement in budgetary review process, budgetary allocation process and in budgetary implementation promoted quality in budget preparation process in Mombasa County. Based on the findings the study recommended that, the county governments needed to fully engage the societies in budgetary preparation process, the move would enable the government to effectively plan and manage its financial resources, support and implement various programs and projects for development bases on priority. County governments needed to periodically carry out budget review. County governments should pay greater attention on budgetary allocation process as this would ensure that those sufficient funds were allocated to every program thus avoiding project deadlocks, and that county governments needed to have an efficient and proper system of accounting to be established so that the information required for the proper implementation for the budgetary control would be available on time.  In future there is need to conduct an assessment on effect of citizen participation and service delivery in devolved government.