© 2022, Electromagnetics Academy. All rights reserved.—This study investigates several substantial questions arising in the diffraction by circular surfaces with the fractional boundary condition, which is the generalization of Dirichlet and Neumann boundary conditions. The study analyses the electromagnetic E-polarized plane wave diffraction by a slotted circular cylinder with the fractional boundary condition. For the first time, the fractional boundary condition regarding circular geometries is employed in the literature. The resonance characteristics for different boundary conditions, angle of incidence, and aperture sizes are analyzed. The new resonances are observed when the surface is different from the perfect electric or magnetic conducting surface.