The　separation　behavior　of　a　variety　of　emerging　contaminants,　including　nine　antibiotics　and　six　estrogens　commonly　reported　in　natural　environment,　by　four　commercial　nanofiltration　and　reverse　osmosis　(NF/RO)　membranes　at　various　water　conditions　(pH,　concentration)　was　investigated.　The　contaminant　rejection　at　pH　6.0　followed　a　decreasing　trend　of　XLE　(94%-100%)　approximate　to　NF90　(88%-100%)　＞　NF270　(25%-85%)　＞　DL　(16%-75%).　The　dense　structures　of　NF90　and　XLE　reflected　by　their　small　effective　pore　radii　(0.30-0.31　nm)　contributed　mainly　to　their　high　rejection,　demonstrating　the　important　role　of　size　exclusion.　For　the　negatively　charged　loose　NF270　and　DL　membranes　(0.40-0.45　nm),　charge　repulsion　made　additional　contribution,　which　is　markedly　reflected　by　their　greater　rejection　to　charged　antibiotics　than　neutral　estrogens　(45%-85%　vs.　25%-60%　by　NF270).　The　correlation　between　rejection　data　and　normalized　molecular　sizes　at　pH　4.0　and　9.0　intuitively　demonstrated　the　individual　role　of　size　exclusion　and　charge　repulsion.　The　adsorption　by　membranes　was　mainly　responsible　for　the　initial　compound　reduction　in　feedwater　by　6%-25%　within　3　h,　while　only　0.3%-5.6%　was　attributed　to　self-degradation.　The　adsorption　capacity　was　determined,　which　might　be　mainly　governed　by　hydrophobic　interaction.　The　resolved　controlling　factors　and　mechanisms　will　contribute　to　the　accurate　prediction　and　membrane　selection　for　trace　contaminant　removal　by　membrane　process.