Leaf traits reflect use-efficiency strategies in plants. The manner in which leaf traits change within or across species can profoundly affect plant growth, reproduction and ecosystem function. The morphological characteristics of plant leaves are greatly influenced by environmental factors associated with climate and light. Morphological plasticity plays an important role in resource acquisition of plants and variations in leaf trait is of major importance for plant adjustment to resource availability. Changes in temperature and rainfall patterns are predicted to significantly influence morphological plasticity of plant leaves. Leaf morphology of native vegetation has often been interpreted as a sensitive indicator of environmental conditions. The relationship between climate and leaf plasticity is universal and particularly important in certain ecosystems, because of their enormous size and correspondingly vast stores of carbon. Tree ecologists with an interest in leaf dynamics have typically concentrated on assessing a limited number of variables, such as leaf length and width, leaf area and leaf weight. However, assessing the leaf dynamics of forest trees is especially challenging since turnover is often high and there is abundant variation in leaf phenotypic characteristics between and within individuals, populations and species. The correlation between leaf length and leaf width and changes of leaf mass per area (LMA) were studied in seedlings of Elaeocarpus sylvestris, Mytilaria laosensis, Cinnamomum camphora, Camellia semiserata, Ormosia pinnata and Castanopsis hystrix, in order to understand change of leaf shape of the six broadleaf seedlings and climate effects on their leaf changes. The very significant correlation existed between leaf length and leaf width of the six seedlings. The month changes of correlative coefficients of most seedlings were intimate with season change. The six seedlings were divided into two types according to leaf similarity change: a), correlation change with season including E. sylvestris, C. semiserata, O. pinnata and C. hystrix; b), steady correlation including C. camphora and M. laosensis. The correlation between leaf length and leaf width changed with rainfall amount according to a linear relationship, and there was a binomial relationship between the correlation and mean temperature as well as between the correlation and illumination time. The LMA changed with seedling species and season and the change was great in the first half year and small in the second half year. The LMA of young leaf was greater than old leaf in the first half year whereas it was close to that of old leaf in the second half year. The change in LMA of old leaf for the six seedlings was small throughout whole year whereas that of young leaf in the first half year was greater than in the second half year. In the first half year the LMA of young leaf for the same seedling was greater than old leaf, whereas they were the similar to each other in the second half year. The LMA of young and old leaves of C. semiserata seedlings was significantly greater than that of other seedlings. The LMA of the six seedlings changed with rainfall amount, mean temperature and illumination time according to a binomial relationship.