Nanofiltration　(NF)　is　an　effective　method　for　removing　trace　organic　compounds　(TrOCs)　from　drinking　and　reused　water.　However,　chemical　cleaning　of　NF　membranes　may　impact　their　properties,　leading　to　a　decrease　in　TrOCs　rejection.　To　better　understand　the　mechanisms　behind　changes　in　membrane　rejection　after　chemical　cleaning,　we　investigated　the　changes　in　surface　properties　and　TrOCs　rejection　of　two　commercial　membranes　(NF270　and　NF90)　after　urea/　hydrochloric　acid　(HCl)　cleaning,　and　compared　them　to　conventional　sodium　hydroxide　(NaOH)/HCl　cleaning.　The　findings　indicated　that　urea　cleaning　increased　the　membrane　pore　size　and　hydrophilicity　while　marginally　affecting　membrane　crosslinking　and　zeta　potential.　Possibly　due　to　the　thicker　and　denser　active　layer　of　NF90,　neither　urea-based　nor　NaOH-based　cleaning　had　a　significant　impact　on　its　TrOCs　rejection　and　permeability.　In　contrast,　NF270　was　more　susceptible　to　chemical　cleaning,　and　urea-based　cleaning　had　less　impact　on　its　TrOCs　rejection　than　NaOH-based　cleaning.　Although　urea　cleaning　increased　the　pore　size　of　the　NF270　membrane,　its　pore　size　recovered　well　after　HCl　cleaning,　resulting　in　good　recovery　of　the　rejection　of　hydrophilic　neutral　TrOCs.　Moreover,　urea　cleaning　had　limited　effects　on　the　electrical　properties　of　the　NF270　and　might　enhance　the　hydrophilicity　of　the　membrane,　resulting　in　full　recovery　of　the　rejection　of　hydrophobic　and　negatively　charged　TrOCs　after　urea/HCl　cleaning.　©　2023　Elsevier　B.V.