A miniature dissolved oxygen sensor is fabricated using photolithographic reduction and thick-film metallization techniques. This sensor has a multiple-cathode configuration and is operated in a three-electrode potentiostatic mode. Evaluation of the sensor characteristics was undertaken and the results are promising. Calibration of the sensor over the oxygen concentration range of 1.14–8.22 ppm (~ 23– 160 mmHg P02) shows a good linear relationship between the reducing current of the sensor and the dissolved oxygen concentration in physiologic saline solution. The current output of the sensor is temperature dependent and is approximately 2.5 percent current output per degree centigrade. The pH value in the test medium does not affect the current output of the sensor but shows an extension of the plateau region of the polarogram. Long-term testing of the sensor indicates that the sensor can be repeatedly used for up to 10 days. There is, however, a variation of ±2.5 to ±7.5 percent in sensor output from the calibration curve as compared with the initial calibration. The sensor is used without any membrane and is flow sensitive. Preliminary tests of the sensor in outdated whole blood also show good response.