This paper presents a discrete-time sliding mode controller based on fuzzy logic for high performance single-phase UPS inverters capable of maintaining low harmonic distortion in response to nonlinear loads. The discrete-time sliding mode control suits for digital realization due to its finite sampling frequency. Also, an algorithm for uncertainty estimation, incorporating with fuzzy tuning technique, is developed. The dynamics of the switching function can be driven to the origin and the stability of this control system is guaranteed. The proposed control scheme has been implemented using a dSPACE DSP. Experimental results on a UPS inverter prototype show that the proposed control scheme can achieve low total harmonics distortion during steady-state operation as well as fast transient response.