Gibberellin 2-oxidase (GA 2-oxidase) plays very important roles in plant growth and development. In this study, the AtGA2ox8 gene, derived from Arabidopsis (Arabidopsis thaliana), was transformed and over-expressed in rapeseed (Brassica napus L.) to assess the role of AtGA2ox8 in biomass accumulation and lignification in plants. The transgenic plants, identified by resistant selection, polymerase chain reaction (PCR) and reverse-transcription PCR (RT-PCR) analyses, and green fluorescence examination, showed growth retardation, flowering delay, and dwarf stature. The fresh weight and dry weight in transgenic lines were about 21% and 29% lower than those in wild type (WT), respectively, and the fresh to dry weight ratios were higher than that of WT. Quantitative measurements demonstrated that the lignin content in transgenic lines decreased by 10%-20%, and histochemical staining results also showed reduced lignification in transgenic lines. Quantitative real-time PCR analysis indicated that the transcript levels of lignin biosynthetic genes in transgenic lines were markedly decreased and were consistent with the reduced lignification. These results suggest that the reduced biomass accumulation and lignification in the AtGA2ox8 over-expression rapeseed might be due to altered lignin biosynthetic gene expression.