Composite　nanofiber　membranes　based　on　biodegradable　poly(lactic　acid)　(PLA)　and　cellulose　nanofibrils　(CNF)　were　produced　via　electrospinning.　The　influence　of　CNF　content　on　the　morphology,　thermal　properties,　and　mechanical　properties　of　PLA/CNF　composite　nanofiber　membranes　were　characterized　by　field　scanning　electron　microscopy　(FE-SEM),　differential　scanning　calorimetry　(DSC),　thermogravimetric　analysis　(TGA),　and　dynamic　mechanical　analysis　(DMA),　respectively.　The　results　show　that　the　PLA/CNF　composite　nanofibers　with　smooth,　free-bead　surface　can　be　successfully　fabricated　with　various　CNF　contents.　The　introduction　of　CNF　is　an　effective　approach　to　improve　the　crystalline　ability,　thermal　stability　and　mechanical　properties　for　PLA/CNF　composite　fibers.　The　Young’s　moduli　and　tensile　strength　of　the　PLA/CNF　composite　nanofiber　reach　106.6　MPa　and　2.7　MPa　when　the　CNF　content　is　3%,　respectively,　which　are　one　times　higher　and　1.5　times　than　those　of　pure　PLA　nanofiber.　Additionally,　the　water　contact　angle　of　PLA/CNF　composite　nanofiber　membranes　decreases　with　the　increase　of　the　CNF　loading,　resulting　in　the　enhancement　of　their　hydrophilicity.　©　2019,　Wuhan　University　of　Technology　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.