Chilling stress may reduce plant growth by affecting physiological and metabolic processes. It is well known that that a symbiotic association of plant roots with arbuscular mycorrhizal fungi (AMF) improves plant cold tolerance and related studies have received extensive attention during the last decade. Root colonization by AMF might strengthen the ability of cold tolerance in plants through attenuating membrane lipid peroxidation and plasma membrane permeability, and increasing osmolyte accumulation as well. Among a large number of vegetable crops which could be infected by AM fungi, cucumber is relatively easy to establish symbiotic associations with vesicular arbuscular mycorrhizae(VAM). Previous studies have reported the relief of chilling stress through the use of AMF. However, these were more focused on plant growth and chlorophyll parameters. The biochemical mechanism underlying AMF-mediated low temperature tolerance in vegetable crops warrants further in depth investigation. Under greenhouse condition, the combined effects of AM fungi and low temperature on cucumber seedlings were investigated with respects to assimilate accumulation, photosynthetic rate, carboxylation efficiency, activities of antioxidant enzymes and related gene expression. AMF inoculums used in this study consisted of spores, soil, hyphae and infected maize root fragment from a stock culture of Glomus mossea-2, which were propagated by AMF inoculums. The experimental design consisted of four treatments crossing two mycorrhizal inoculations levels (non-AMF and Glomus mossea-2) with two temperature levels (25/15℃, 15/10℃). The inoculated dosage was 20 g of inoculums per pot containing. Repeat 3 times for each treatment, 10 plants per replicate.The results showed that mycorrhizal colonization abilities and mycorrhizal dependency were significantly inhibited by low temperature. Fungal growth accelerated considerably during the period from 30 d to 45 d after inoculation with AMF. At 45 d after inoculation, mycorrhizal colonization ratio on cucumber roots was 42.68% and 32.15% under room temperature and low temperature, respectively, Mycorrhizal dependency was 21.42% and 5.46% under room temperature and low temperature respectively and this indicated a significant reduction in low temperature (P<0.05). Regardless of the temperature, the root-shoot ratio, total dry weight and fresh weight of AMF inoculated seedlings were significantly higher than that of the non-AMF control (P<0.05). The photosynthesis, root activity, carboxylation efficiency, contents of chlorophyll and soluble proteins increased by 23.67%, 29.13%, 33.10% and 11.78% compared with the control under low temperature. Moreover, Malondialdehyde content stayed at relatively low level in AMF-treated seedlings. On the other hand, the AMF treatment enhanced the activities and transcript levels of antioxidant enzymes. Superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), ascorbate peroxidase (APX) expressions of the AMF-inoculated seedlings were increased by 1.35, 1.44, 1.70, 2.46 folds respectively compared with CK₁. Under chilling stress, the expression levels of SOD, G-POD, CAT and APX genes in the AMF-inoculated seedling were increased by 1.68, 1.37, 1.52 and 1.83 folds respectively in control under normal temperature(CK₁) compared with those under low temperature(CK₂). These results indicated that antioxidant enzymes might play a crucial role in AMF-mediated tolerance to chilling stress, thereby maintaining a high photosynthetic capacity in cucumber seedlings.