A novel novel dmit2- salt: ［(C3H7)4N］［Au(C3S5)2］ was synthesized. Its acetonitrile solution with concentration 1.0 ×10-3 mol/L was prepared. The thin film with ［(C3H7)4N］［Au(C3S5)2］-doped in PMMA was fabricated spin-coating on a quartz substrate. The third-order optical nonlinearities of sample solution and film were investigated by using the laser Z-scan technique with 20 ps pulses width at 1 064 nm. The experimental results show that the third-order nonlinear susceptibility χ(3) improves an approximate 3 orders of magnitude by the PrAu film over the solution. The nonlinear refraction coefficient n2 and the third-order nonlinear susceptibility χ(3) of the PrAu film were obtained to be 1.76×10-15 m2/W and 9.37×10-10 esu, respectively. The results suggest that PrAu will be a promising material for all-optical switching devices.