Poly (ρ-phenylene vinylene) (PPV) derivatives with symmetrical and asymmetrical alkoxyl substitutes including poly (2-methoxy-5-butoxy)-ρ-phenylene vinylene (PMOBOPV),poly (2-methoxy-5-hexyloxy)-ρ-phenylene vinylene (PMOHOPV),poly (2,5-dibutoxy)-ρ-phenylene vinylene (PDBOPV) and poly (2,5-dihexyloxy)-ρ-phenylene vinylene (PDHOPV) were prepared through bisetherification,chloromethylation and dehydrochlorination reaction and characterized by UV-Visible absorption spectrum. The results revealed that the conjugated absorption peak of PMOBOPV,PMOHOPV,PDBOPV and PDHOPV assigned to π→π^* transition of π electrons were located at 491 nm,495 nm,504 nm and 510 nm and the optical bandgaps were also measured to be around 2.23 eV,2.18 eV,2.12 eV and 2.07 eV respectively. The third-order nonlinear optical susceptibilities (χ⁽³⁾) of PPV derivatives were studied by degenerate four-wave mixing technique and the effects of molecular structure on third-order optical nonlinearities of PPV derivatives were also investigated. The experimental results showed that the resonant χ⁽³⁾ values at 532 nm of PMOBOPV,PMOHOPV,PDBOPV and PDHOPV were 3.45 × 10^-10,5.13 × 10^-10,7.15 × 10^-10 and 9.61 × 10^-10 esu,and the corresponding off-resonate χ⁽³⁾ values at 1064 nm were 1.09 × 10^-11,1.42 × 10^-11,1.62 × 10^-11 and 2.14 × 10^-11 esu respectively.