Changium smyrnioides Wolff, a monotypic species in Umbellaceae, has a narrow distribution area, which can only be found in Yangtze Rive basin in China, and its seedling is rare in natural habitat. Anthriscus sylvestri (L.) Hoffm., a ruderal in Europe and China, is one of the classical clonal caespitose plants and distributed widely. A. sylvestri has been investigated in a wide ecolog ical scope in Europe for its powful progenitive capacity and tolerance of severe environmental conditions. C. smyrnioides is an endangered plant, A. sylve stri is a ruderal, however, both species have similar lifestyle. Light is an i mportant environmental factor for all plants, and the distribution and growth of C. smyrnioides are limited by light. Morphological plasticity plays an impo rtant role in light acquisition of plants and variations in size and placement o f light-acquiring organs such as leaf, which is sensitive to light availability . In this study we investigated the influence of light on the two species seedli ngs growth. Three light intensity treatments, i.e. 100％ relative light intensit y（S₁₀₀）, 65％ relative light intensity（S₆₅）and 25％ relative lig ht intensity（S₂₅）, were established. Results showed that light was a ver y important factor affecting C. smyrnioides seedling growth, but not for A . sylvestri. C. smyrnioides seedling growth had a significant difference under different light indensity. Under S₆₅ C. smyrnioides seedling grew fas test, and the height, crown amplitude, leaf length, leaf width, leaf biomass and root biomass achieved the highest valuees. The total biomass of C. smyrnioide s seedling under S₆₅ was twice than seedling under S₁₀₀ and trinal times than under S25. Leaf biomass of A. sylvestri seedling was incr eased with the decrease of light intensity, and the leaf biomass was the highest under S25. Root biomass of A. sylvestri seedling grew fastest under S ₆₅, just as C. smyrnioides seedling. Difference of relative growth rat ios ( RGR ) of C. smyrnioides seedling was significant under three treatme nts, and the RGR under S65 was significantly higher than the other treatme nts. The RGR of A. sylvestri had no difference among three light treatments. The RGR of C. smyrnioides seedling was significantly higher than of A. sy lves tri. The total biomass of C. smyrnioides seedling was 1/3 to 1/8 of A. s ylvestri, that meant it was a species with slowly growing speed during junior phase relative to A. sylvestri.