Bî-seng-bu̍t (微生物) sī ba̍k-chiu khoàⁿ bē tio̍h ê sió-hêng seng-bu̍t. Gián-kiù bî-seng-bu̍t ê ha̍k-būn hō chò bî-seng-bu̍t-ha̍k. Bî-seng-bu̍t ê chéng-lūi chē-chē, pau-koah sè-khún, ko͘, kó͘-seng-khún (archaea), goân-seng-seng-bu̍t (protists), sīm-chì chi̍t-koá si̍t-bu̍t, tōng-bu̍t mā ū chún-sǹg. In bô pau-hâm pēⁿ-to̍k, prion chit-khoán hui-seng-bu̍t. Bî-seng-bu̍t toā-hūn sī tan-sè-pau (unicellular), ū-koá sī to-sè-pau.

Anton van Leeuwenhoek1675 nî iōng i siat-kè ê hián-bî-kiàⁿ hoat-kiàn tio̍h bî-seng-bu̍t ê chûn-chāi.