Minois nagasawae (Matsumua) is a relict species inhabiting the alpine zones of Taiwan. The genus belongs to the “Satyrus series,” which is primarily Eurasian in distribution. We present the first observations of its host plants, biology, and morphology of the early stages. Two species of grasses, Brachypodium kawakamii and Deschampsia caespitosa (both Poaceae), were recorded as larval host plants. We confirmed that the eggs of M. nagasawae are dropped freely without attachment to the substrate and that five instars are required to complete larval development. Obligate winter diapause occurs in the larval stage, usually in the first or second instar. This biology is highly consistent with the closely related, temperate species Minois dryas (Scopoli), suggesting that M. nagasawae retains biological traits adapted to cool habitats even though it is restricted to an island dominated by a subtropical climate.