The sensitive single-beam technigue for mrasuring the nonlinear refractive index has been studisd for the cases that matorials have varied linear absosption ,It is found that the inereament of lines abserption will smear the solution of this technique and lead the sensihility lower. The experimenfal a sults of the nonlinear refractive index meamrement of a kind of polymer material deped with chlorphyll-α are also reported. The is n2≈3.4×10-9esu. Analysis shows that nonlinear refraotion is caused by π-electrons effects.