Abstract: An automated pH monitoring and controlling system for hydroponic system was developed, calibrated and validated in this study. The automated monitoring and controlling system was developed to monitor and control the pH of nutrient solution in hydroponic system. The greenhouse available at the Center for Hydroponics and Aquaponics Technology (CHAT) and locally available materials and hardware for the hydroponics and automation were used in the development of the system. These devices were designed and assembled based on the conceptual framework of the study. The pH sensor sends signal to the microcontroller which triggers the adding of acid/base solution and turning on/off of the mixer. The instruments used were calibrated prior to the performance evaluation and obtained calibration equation for the pH sensor is y = 0.91x+0.91. Validation of the automated pH monitoring and controlling system was done and the recorded maximum pH is 6.54 and minimum pH of 6.0. The lettuce planted during the validation has an average height of 14.61 cm and the average leaf count of 12 for the lettuce crops during the 4th week after planting. A total of 4.78 kg of lettuce crop was harvested with an average of 20.6 g per lettuce crop was obtained. Based on the performance evaluation and validation done on the automated pH monitoring and controlling system, it was found to be reliable. This system becomes useful in reducing labor cost and allows for real-time monitoring of pH, therefore, increasing farmer’s crop productivity and income.