The extraction conditions of Laoshan green tea extracts were optimised by response surface method. In vitro, the MDA, NO, TNF-α, and IL-6 levels were significantly inhibited and SOD level was increased after Laoshan green tea polysaccharides (GTPS) administration in RAW264.7 cells induced by LPS. Besides, GTPS also suppressed NF-κB, TNF-α and IL-6 expression. In vivo, the spleen and liver organ indices, and TNF-α, IL-6, ALT and AST levels were significantly inhibited after GTPS treatment in LPS-induced mice. The liver injury was also significantly alleviated. Overall, GTPS may be therapeutic reagents to attenuate inflammation and liver injury. GTPS were acidic galactose-rich heteropolysaccharides containing sulphate groups. GTPS were composed of Man, GalN, GlcA, Glc, Gal, and Ara in molar ratios of 1.66:1.00:6.92:5.44:46.71:12.08 with the molecular weights of 81.73, 659.87, and 1304.39 kDa.