Abstract: Perennial ryegrass (Lolium perenne), a graminaceous crop, is one of the most widely distributed grass in the temperate regions for forage and turf. However, its transformation mediated by Agrobacterium tumefaciens is largely recalcitrant and lagged. In this paper, an improved method for perennial ryegrass mediated by A. tumefaciens was developed. And the transgenic plants were successfully obtained. Embryogenic calli induced from mature embryos of a perennial ryegrass variety Tove were transformed by A. tumefaciens strain EHA105 containing the plasmid pCAMBIA2301. In this protocol, 0.1 mol/L mannitol or 5 mg/L silver nitrate (AgNO₃) were added in preculture and coculture media. After selected with paromomycin and detected with PCR and GUS expression, we got 38 transgenic plants in all. The transgenic frequency was increased when 0.1 mol/L mannitol or 5 mg/L AgNO₃ or 5 mg/L AgNO₃+0.1 mol/L mannitol was added in the pre-cultivation and co-cultivation media, which was 1.96, 1.59 and 2.95 times compared to control respectively. Moreover, the transgenic frequency was highest when the two materials were jointly used. The results indicated that mannitol and AgNO₃ could improve the A. tumefaciens mediated transformation in perennial ryegrass evidently.