A separator for a lithium ion secondary battery, comprising a porous base material containing polyolefin, and a porous layer containing a vinylidene fluoride resin as a main component provided on at least one surface of the porous base material is excellent in electrolytic solution retention properties, adhesion and bondability to electrodes, and dimensional stability, and also has high and uniform ionic conductivity, reduced interfacial resistance to electrodes, and shutdown properties. A lithium ion secondary battery having excellent capacity characteristics, charge and discharge characteristics, cycle characteristics, safety and reliability can be provided by using the separator.