Electromagnetic scattering from multiple slits in a thick perfect conducting plane is investigated. The Fourier transform and the mode matching are used to obtain the simultaneous equations. The simultaneous equations are solved to obtain a series solution which reduces to a closed-form in high-frequency limit. The transmission coefficients are represented in fast convergent series which are efficient for numerical computations. Numerical computations are performed to illustrate their scattering behaviors in terms of frequency, slit size, and slit number.