The single fiber transverse compression test (SFTCT) is applied to KEVLAR and TWARON poly (para-phenyleneterephthalamide) fibers, both continuous filament and staple, and of varying denier and heat-treatment, as well as M5 rigid-rod fibers. Resulting force-deflection curves are analyzed by a Hertzian contact model, to give the effective transverse modulus, and estimate the stress state in the fiber at the onset of yield. Confocal microscopy and finite element simulation are used in conjunction with SFTCT to describe the inelastic, transverse deformation of PPTA. The effects of skin-core structure and anisotropy in the fiber cross-section are discussed.