Abstract Molybdenum(V) forms complexes with the following α-hydroxycarboxylic acids- l -mandelic, l -lactic, d -tartaric, l -malic, d -glucosaccharic, d -glyceric, d -erythronic, l -threonic, d -ribonic, d -lyxonic, l -arabinonic, d -xylonic, d -allonic, d -gluconic, d -talonic, d -mannonic, l -rhamnonic, d -gulonic and d -galactonic acids. These compounds were identified by the formation of optically active species in solution with Cotton effects about 22·0, 25·0 and 32·0 kK. The complexes exist in the pH range 2·5–8·5 with the exceptions of l -mandelic, l -lactic and d -glyceric acids whose complexes only exist about pH3. d -Tartaric and l -malic acids also formed complexes in 2N acid solution.