Cellulosic　nanocomposite　membranes　were　prepared　by　incorporation　of　cellulose　nanocrystals　(CNCs)　into　a　hydroxypropyl　cellulose　(HPC)　matrix　using　a　mixing/evaporation　technique.　CNCs　were　obtained　from　filter　paper　using　the　sulfuric　acid　hydrolysis　method　with　the　aid　of　ultrasonication.　The　relationship　between　the　microstructure　and　mechanical　properties　of　the　CNCs/HPC　nanocomposite　membranes　was　studied.　Scanning　electron　microscopy　showed　that　the　CNCs　were　well　dispersed　in　the　HPC　matrix,　and　the　fracture　surface　demonstrated　a　fibrous　characteristic.　With　increasing　CNCs　content,　the　tensile　strength　and　Young＇s　modulus　of　the　CNCs/HPC　nanocomposite　membranes　gradually　increased.　At　5　wt%　content　of　CNCs,　the　strength　was　increased　by　525　%　and　the　Young＇s　modulus　by　124　%　compared　with　pure　HPC　membrane.　Moreover,　the　effect　of　the　phase　change　of　HPC　on　the　mechanical　properties　of　the　CNCs5wt%/HPC　nanocomposite　membranes　and　the　corresponding　mechanism　were　also　studied.