Along with the transfer of rural labor and the prevalence of simplified cultivation rice technologies in the 2000s, weedy rice has caused serious damage to rice production and commercial quality in many regions of Heilongjiang, Liaoning Ningxia, Jiangsu, Shanghai, Guangdong and other Provinces in China, and over 600,000 ha rice were infested every year.Because of no-tillage farming technique including interplanting rice with wheat stubble and dry direct seeding of rice has been extensively used, the total infesting area by weedy rice reached to ~200,000 ha in Taizhou and Yangzhou of central Jiangsu Province in 2008, which accounted for about 25% of total acreage of direct sowing rice.To clearly classify Jiangsu weedy rice, 23 distinct weedy rice samples collected from Jiangsu were grown.Morphological and biological characteristics including coleoptile color, leaf sheath color, tillering number,plant height, ratio (length/width) of the reversed 2nd leaf and flag leaf, heading date, panicle exsertion, panicle type, spike length ,effective panicles, glume color, hull color, awn length, ratio (length/width) of grain, seed-setting percentage, 1000-grain weight and pericarp color of the all samples were investigated during the entire growing period.The results showed that the plant height and leaf size of weedy rice was closer to that of cultivated rice Ningjing 1 at the seedling stage.However, it was significantly different from the cultivated rice after the tillering stage.Weedy rice has an obvious and comprehensive advantage of fast growth and high weed competition at late stage.Its average values of plant height and tiller number were 0.8-28cm and 6.1 higher than that of cultivated rice, respectively.However, seed setting percentage, 1000-grain weight and ratio (length/width) of grain were 15%, 7g and 1.3 lower than that of cultivated rice, respectively.Most of weedy rice plants were tall with upright panicles and its maturity was about 15 days earlier comparing to the rice varieties.The majority of weedy rice samples showed red pericarp and straw to dark brown colored hull.Consequently, our study suggested that Jiangsu weedy rice might be divided into 8 biotypes.The characteristics of biotype A (52.2%) showed upright plant type, straw color hull, red pericarp and awnless, was taller plant height than that of cultivated rice.The characteristics of biotype B (13%), biotype C (8.7%), biotype D (8.7%) and biotype G (4.3%) were identical to that of biotype A,except for white pericarp (biotype B), awned seed (biotype C), lower plant height than cultivated rice (biotype D) and loose plant type (biotype G).Biotype E (4.3%) was different from biotype D with black brown hull.Biotype F (4.3%) was closer to that biotype E except for lower plant height than cultivated rice.Biotype H (4.3%) was different from biotype G with white pericarp and awned seed.