Abstract: In order to investigate the physiological characteristics of Lysimachia plants in high temperatures, a pot seedling experiment in artificial climatic chamber was conducted using four Lysimachia species. The effect of high-temperature stress on plasma relative permeability, protective enzyme activity and leaf osmoregulatory molecules in plants were analyzed. The study shows that with the high-temperature stress strengthening, the membrane damages and leaf cell membrane permeability increases. SOD and POD activities increase under the moderately high-temperature stress, while decline under extremely high-temperature stress. Total chlorophyll content, proline content and leaf soluble protein increase under high-temperature stress, though the trends differ for different species. Analysis of physiological and biochemical characters suggests that high-temperature resistance ability of L. alfredii and L. christinae var huaye is high and that of L. nummularia ‘Aurea’ and L. congestiflora is low.