Experimental results of a dielectric-loaded free-electron maser (FEM) oscillator in a stripline structure are presented. The table-top oscillator experiment employs a low-energy electron beam (8 keV, 0.5 A) and a folded-foil wiggler (2 cm period). The waveguide consists of dielectric slabs and metal striplines along the side walls of a rectangular tube. The metallic striplines protect the dielectric slabs attached to them from the electron beam, and support a quasi-TEM mode in the waveguide. The effective dielectric constant of the dominant odd quasi-TEM mode is measured as ɛeff ≅ 8. The oscillator operates in a frequency range of 3-5 GHz, in agreement with the tuning relation of the slow-wave dielectric-loaded free-electron maser.