The effect of temperature during growth on the photosynthetic characteristics of soybean (Glycine max [L.] Merrill) was studied using cultivars from Maturity Group 00 (Altona, Fiskeby V, Flambeau, Maple Presto, McCall) and MG VIII (Hampton 266–A, Hardee, Johnston, Kirby). In one experiment plants were grown with 950 μmol m−2s−1 photosynthetic photon flux density (PPFD) at 18, 20, 25 and 30 °C. When grown at 20 °C, MG 00 cultivars averaged significantly higher rates of photosynthesis measured at 25 °C and saturating PPFD than did MG VIII cultivars. Cultivars were also grown with a PPFD of 540 μmol m−1 at 17.5, 20.0, 22.5 and 25.0 °C. Maturity Group 00 cultivars averaged higher photosynthetic rates than MG VIII cultivars at the 20.0 and 22.5 °C growth temperatures. The other growth environments produced no significant differences between maturity groups. Photosynthetic rates differed between cultivars, but not maturity groups, after exposure to a single night with a gradual temperature decline to 8 °C. Photosynthetic rates recovered in 28 h. Two cultivars, Altona and Johnston, were grown outdoors at three times during one growing season at Beltsville, and their maximum photosynthetic rates changed depending on the temperatures during leaf development, in agreement with the data from the controlled environment studies.Key words: Soybean, Glycine max [L.] Merrill, photosynthesis, temperature, acclimation