Biodiesel is an alternative fuel produced by the transesterification of vegetable oils in the presence of homogeneous or heterogeneous catalysts. Herein, we report the transesterification of vegetable oils using CaO nanoparticles supported on a polydopamine-coated hyper-crosslinked polymer, CaO@PDA-HCP as a heterogeneous catalyst. The effect of CaO-nanoparticle concentration (5-20 wt%) on catalysis performance was investigated, and the PDA-HCP surface was examined by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Basicity was shown to greatly influence the methyl ester content, and the best catalyst (15 wt% CaO) was demonstrated to be reusable without any loss of activity.