The transient photochemical behavior of xanthone(XAN) in 1-butyl-3-methyl imidazolium hexafluoride phosphate ionic liquid (［bmim］［PF6］) or binary mixed solution with acetonitrile (MeCN) was investigated by nano-second laser photolysis techniques. The spectral blue shift of 3XAN* was observed in the neat ［bmim］［PF6］ or IL/MeCN mixture solution compared to MeCN solution. And the yield was also increased. Moreover, the energy transfer rate constant of XAN and naphthalene (NAP) was affected by the concentrations of ionic liquid. The values decreased rapidly with increasing VIL. For example, the values were 1.2×1010 mol·L-1·s-1 in MeCN, and 1.1×108 mol·L-1·s-1 in ［bmim］［PF6］, respectively. The photo-induced electron transfer between XAN and N,N-dimethylaniline was also investigated by changing the concentrations of ［bmim］［PF6］ in binary solution.