This paper presents Control of UPS inverter Using Fuzzy Gain Scheduling of PI Controller. This control scheme has Double Loop Current Mode Control Scheme in core. This scheme includes two control loops as inner and outer control loops. Inner control loop uses inductor current of inverter filter as feedback while outer control loop uses inverter output voltage as feedback. Fuzzy Logic Controller (FLC) is used to adjust the voltage loop PI controller parameters. The voltage error, e and its derivative, de are used as input variables of the FLC. In this study, Double Loop Current Mode Control and Fuzzy Gain Scheduling of PI Controller are simulated digitally using PSIM and C++ under linear, rectifier type nonlinear and fluorescent loads. And the results show that Fuzzy Gain Scheduling of PI Controller can provide low THD and better regulation quality especially under rectifier type nonlinear and fluorescent loads.