Waterproof breathable membranes (WBMs) are widely employed in various fields. However, the construction of fluorine-free WBMs with excellent waterproofness using simple strategies remains a challenge. Herein, we report waterproof breathable polyethylene terephthalate (PET) fibrous membranes embedded with fluorine-free hydrophobic polydimethylsiloxane (PDMS) via a simple one-step electrospinning combined with heat treatment techniques. The resultant PET/PDMS membranes with vigorous hydrophobic channels, small apertures and high porosity were constructed by in-situ doping of PDMS, which endowed them with excellent water resistance of 86.9 kPa, good moisture permeability of 5100 g m−2 d−1, desirable air permeability of 6.97 mm s−1, and enhanced mechanical strength of 6.27 MPa. The obtained nanofiber WBMs can be used as an exceptional additional product for a variety of existing applications.