The aim of this study was to investigate the efficacy of navel orange, Citrus sinensis (L.) Osbeck, peel essential oil (NOPEO) for inhibiting spoilage fungi in potato slices. Sixteen different components accounting for 99.79% of the headspace components of NOPEO were identified by gas chromatography–mass spectrometry. d-Limonene was the major component of NOPEO. Antifungal activity of NOPEO was tested in vitro and in vivo against four foodborne fungi. A MIC of NOPEO against the four fungal species was 9.40 μL/mLair. NOPEO provided about 74, 74, 73, and 69% protection against Aspergillus niger, Mucor wutungkiao, Penicillium funiculosum, and Rhizopus oryzae at 2.00 μL/mLair concentration, respectively. NOPEO has been demonstrated to significantly improve the microbiological quality of potato slices.