In this paper, we evaluate the performance degradation of finger type PSJA due to fog. PSJA (Plasma Synthetic Jet Actuator) is jet device which is composed of insulator and two electrodes. It is necessary to verify the weather resistance of the PSJA because this device is intended to be used mainly outdoors. We use the visibility to quantify the density of the fog. We measure the force generated by finger type PSJA operating in a container filled with the fog, and evaluate the dependence on visibility. As a result, we found that the force applied to the finger type PSJA is reduced in dense fog environment.