The objective of this study was to examine the effects of exogenous α-oxoglutarate on leaf proline accumulation, ammonium assimilation and photosynthesis of soybean when exposed to cold stress. To achieve this objective, exogenous α-oxoglutarate was sprayed to potted seedlings of Henong60 and Heinong48 at 0, 2.5, 5.0 and 7.5 mmol/L, identified as A0, A2.5, A5.0, and A7.5, respectively. Leaf samples were collected after cold stress of 24 h (S1 stage) and 48 h (S2 stage). The results indicated that exogenous α-oxoglutarate significantly enhanced leaf GS activity, NADP-GDH activity, glutamate content, proline content and photosynthesis of soybean seedling exposed to cold stress at S1 and S2 stages. The ammonium content in leaf was significantly decreased by exogenous α-oxoglutarate at both stages. 5.0 mmol/L of exogenous α-oxoglutarate is the optimum concentration in this study. Leaf proline content for Henong60 and Heinong48 at A5.0 was 37.53% and 17.96% higher than that at A0 at S1 stage, respectively. Proline content for Henong60 and Heinong48 increased by 28.82% and 12.41% at A5.0 and A0, respectively, at S2 stage. Those results suggested that exogenous α-oxoglutarate could alleviate the adverse effects of cold stress.