This study determined the effectiveness of the Commission on Audit Information System (COA IS) and its effect on the productivity of the COA Regional Office No. IV-A personnel. Specifically, it assessed the effectiveness of the COA IS in terms of system reliability and accessibility, accuracy and timeliness of information, user-friendliness and functionality, data security and integrity, and responsiveness of technical support; the level of employees’ productivity in terms of task completion rate, accuracy of work outputs, time efficiency, quality of work performance, and job satisfaction; and the significant effect of the respondents’ demographic profile and the COA IS on employees’ productivity using weighted mean, standard deviation, Pearson correlation, and regression analysis.It used a descriptive-correlational research design, with a survey questionnaire as the primary data collection tool, administered to 202 personnel of the COA Regional Office No. IV-A who were selected through total enumeration. The gathered data were statistically analyzed to determine the relationship between the effectiveness of the COA IS and employees’ productivity.Findings indicated an overall weighted mean (OWM) of 3.11 for the COA IS, which was verbally equivalent to the respondents’ description “Often”, indicating moderate effectiveness; while employees’ productivity registered an OWM of 2.68, tantamount to their “Agree” responses to the questionnaire statements. Among the COA IS dimensions, data security and integrity received the highest rating (OWM = 2.87), whereas job satisfaction received the lowest rating (OWM = 2.53) among the productivity variables. The results further showed that age, designation, and length of service significantly affected selected dimensions of COA IS effectiveness and employees’ productivity, whereas gender did not. Additionally, the COA IS significantly influences employees’ productivity. It is concluded that the COA IS contributes positively to employees’ productivity and audit performance. It is therefore recommended that COA strengthen system reliability, enhance technical support services, and provide continuous training programs to further improve system effectiveness and employees’ productivity.