A liquid crystal microlens array (LCMLA) with positive and negative focal lengths based on a ring-array patterned electrodes is demonstrated. By carefully designing patterned electrodes with a circular electrode array area and outer ring electrode region area, the switching of the positive and negative lens effect can be easily achieved in a single cell. A positive lens effect appeared when the voltage was applied to the outer ring electrode region and the top substrate. The focal length changed from infinity to 1 mm as the voltage varied from 0 to 3Vrms. A negative lens effect occurred when the voltage was applied to the circular electrode array and the top substrate. The focal length varied from infinity to -1mm when the voltage changed from 0 to 2Vrms. The imaging properties of the LCMLA at different voltages are evaluated. Our LCMLA, with simple structure, low driving voltage, and good stability, has potential applications in optical communication, imaging processing, and displays.