Abstract: Nutrient deficiency and the accompanying weeds are generally the influencing factors of rice growth. In this research, suppression subtractive hybridization (SSH) was used to investigate up-regulating genes in non-allelopathic "Lemont" rice accession respectively in response to low nitrogen condition and accompanying barnyardgrass. The results showed that genes encoding auxin-responsive protein which involved in plant growth and cell cycle regulation, NBS-LRR-like protein, catalase, metallothionein-like protein that involved in stress resistance, and protein metabolism relevant genes were up-regulated under low nitrogen condition. When rice was accompanied with barnyardgrass, genes encode NADH dehydrogenase, ATP-dependent RNA helicase and cytochrome oxidase that relative to plant growth and cell cycle regulation, RING finger family protein and two-component sensor histidine kinase relative to signal transduction, chitinase and glycosyl hydrolases relative to rice resistance were increased expression. The findings suggested that rice survived in low nitrogen supply or barnyardgrass competition by increased expression levels of various genes related with enhancement of resistance and plant growth regulation.