Abstract: An automatic photometric titration analyzer with color change as end point of titration was prepared. The analyzer consisted of reflective photometric sensor (as core), photometric probe, titration device, AT89S52 monolithic circuit, electromagnetic valve, diode and magnetic stirrer. The open design of sensor leaded to detect the absorbance of solution without delay in titration. The analyzer was applied in the determination of acidity of red vinegar, and the results obtained were in consistency with those obtained by potentiometric titration.