Abstract: Changes on relative electric conductivity, soluble sugar, proline (Pro) and malondialdehyde (MDA) in the apical leaves of Oncidium Gower Ramsey, Jin Hui, under low temperatures with varied durations were studied. The results showed that the electric conductivity and Pro content increased with the stress, but MDA decreased with the treatment time. The content of soluble sugars rose initially, and then, declined as the temperature was lowered and the stress continued. The changes on the leaf relative electric conductivity, Pro and MDA induced by the stress showed a consistent pattern suggesting that they could be used as an indicator in evaluating the cold tolerance of an Oncidium plant.