In this article, a multi-input multi-output sliding mode control methodology with constant switching frequency for single-phase quasi-Z-source inverters (qZSI) is proposed. The mathematical model of the entire system is derived in state-space form. The proposed sliding mode control is capable of controlling both dc and ac sides of the system concurrently. Unlike the existing methods, the proposed control does not require proportional-integral controller in the dc-side. Furthermore, it offers several advantages, such as simple implementation, reduced gain requirement, robustness against system parameters, and zero steady-state error in the load voltage. The fixed switching frequency is attained by altering the sliding manifold behavior inside a boundary layer. The power balance equation is used to generate the dc-side inductor current reference. The feasibility of the proposed control method is investigated experimentally when qZSI feeds linear and nonlinear loads.