Chlorophenoxy　acid　herbicides　(CAHs),　which　are　widely　used　on　cereal　crops,　have　become　an　important　pollution　source　in　grains.　In　this　work,　a　highly　hydrophobic　poly　(octadecyl　methacrylate-co-trimethylolpropane　trimethacrylate)　[poly　(OMA-co-TRIM)]　monolithic　column　has　been　specially　prepared　for　hydrophobic　in-tube　solid-phase　microextraction　(SPME)　of　CAHs　in　rice　grains.　Due　to　the　hydrophobicity　of　CAHs　in　acid　conditions,　trace　CAHs　could　be　efficiently　extracted　by　the　prepared　monolith　with　strong　hydrophobic　interaction.　Several　factors　for　online　hydrophobic　in-tube　SPME,　including　the　length　of　the　monolithic　column,　ACN　and　trifluoroacetic　acid　percentage　in　the　sampling　solution,　elution　volume,　and　elution　flow　rate,　were　investigated　with　respect　to　the　extraction　efficiencies　of　CAHs.　Under　the　optimized　conditions,　the　limits　of　detection　of　the　four　CAHs　fell　in　the　range　of　0.9-2.1　μg/kg.　The　calibration　curves　provided　a　wide　linear　range　of　5-600　μg/kg　and　showed　good　linearity.　The　recoveries　of　this　method　ranged　from　87.3%　to　111.6%,　with　relative　standard　deviations　less　than　7.3%.　Using　this　novel,　highly　hydrophobic　poly　(OMA-co-TRIM)　monolith　as　sorbent,　a　simple　and　sensitive　online　in-tube　SPME-HPLC　method　was　proposed　for　analysis　of　CAHs　residue　in　practical　samples　of　rice　grains.　©　2019　by　the　authors.