Studies on the biosynthesis and degradation of biotin-vitamers by microorganisms were reviewed and discussed. The main pathway of biotin biosynthesis by microorganisms is considered to be as follows : pimelic acid→pimelyl CoA→7-keto-8-aminopelargonic acid→7,8-diaminopelargonic acid→desthiobiotin→biotin. All the enzymes which are involved in the reactions from pimelic acid to desthiobiotin have been elucidated. The biosynthesis of biotin has been found to be controlled by biotin via enzyme repression. Biotin, desthiobiotin, and their analogs, are degraded by microorganisms to their corresponding catabolites, with acid side chains 2 or 4 carbon atoms shorter than their biotin-analogs, probably through a β-oxidation reaction. Biotin and desthiobiotin are also synthesized from their β-oxidation products.