An in situ prepared AlI3-poly(ethylene oxide) (PEO) quasi-solid-state electrolyte for dye-sensitized solar cells (DSCs) has been obtained. An intensive interaction between Al3+ ions and oxygen atoms from PEO was studied. The molecular weight of the PEO has been revealed to strongly influence the photovoltaic performance, and PEO 1500 (Mw=1500) can give the highest conversion efficiency among the four kinds of PEOs. This dependence was further verified by electrochemical impedance spectra. After being optimized, the DSCs using the AlI3-PEO electrolyte showed 6.30% of conversion efficiency.