In this paper, the effects of the superstrate chirality on the resonant frequency and bandwidth of rectangular microstrip patch in a substrate-superstrate configuration are investigated. The problem is rigorously formulated via integral equation. This equation is solved using Galerkin’s moment method; the complex resonance frequencies for TM₀₁ mode are studied with sinusoidal basis functions. The obtained theoretical results show that the decrease is more important for high permittivity loading and negative chirality element.