University campuses often contain contiguous areas of urban green space (UGS) which are otherwise scarce in large cities and, thus, may provide critical habitat for numerous species. In this study, we evaluate butterfly and plant diversity at Chiba University in Japan from five UGS types, including intensive green roofs, meadows, roadsides, open spaces, and community gardens. Surveying non-destructively every two weeks from June to November 2010, we identified 707 individual butterflies to 25 species from five families, including red-listed species (e.g. Parantica sita Kollar, 1844). However, one species, Pseudozizeeria maha Kollar, 1848, represented over 50% of all individuals surveyed. Butterflies in the family Papilionidae showed strong preference for roadside habitat, indicating the importance of ‘butterfly flyways’ and contiguous habitat corridors on University campuses. Butterfly richness and abundance was significantly different between UGS types and highest in the community garden and roadsides. We recorded 70 garden plant species and 117 spontaneous plant species (which grew opportunistically, without design input), of which 58% were native. Total plant richness was positively correlated with butterfly species richness, and non-native spontaneous plant species richness was positively correlated with butterfly richness, abundance, diversity, and evenness. Additionally, 76% of the spontaneous species identified were determined to be used by butterflies as larval hosts or for adult feeding. Identification of spontaneous plant species and use of selective weeding should be included in landscape management planning on campuses to promote butterflies, which can act as ambassadors for biodiversity conservation and help connect people to nature.