A facile route for fabrication of polypropylene separators for lithium-ion batteries with high elongation and strong puncture resistance has been proposed in this work. Polypropylene separators immersed in paraffin wax have been prepared to introduce small molecules into separators. The influence of small molecules on mechanical properties of separators is studied in this work. The elongation at break stretched in the transverse direction of separators significantly increases for more than 300% while the puncture depth and force increases 50% after treatment with paraffin wax for 2 h. Meanwhile, no clear change of the pore structure can be seen after the treatment. The mechanism behind it has been discussed as well. Moreover, comprehensive performance of batteries equipped with modified separators has been evaluated. The modified separators exhibit same electrochemical performances compared to original separators. Generally, paraffin modification is a facile and effective route for mechanical enhancement of separators without sacrificing comprehensive electrochemical properties.