The　total　flow　time　of　an　hourglass　is　depending　on　the　effective　diameter　of　the　neck　pipe　if　the　amount　of　sand　is　fixed.　Molecularly　imprinted　polymers　(MIPs)　can　recognize　the　targets　with　high　selectivity.　In　this　study,　these　characters　had　been　combined　together　and　applied　to　develop　a　sensor　using　a　simple　timer　as　readout　for　the　first　time.　Hydroxy　polychlorinated　biphenyls　(OH-PCBs)　had　been　chosen　as　the　model　target.　If　the　MIPs　had　bounded　with　the　OH-PCBs,　the　imprinting　cavity　of　the　MIPs　can　be　blocked　by　the　target,　and　the　effective　pore　diameter　of　the　column　decreased.　When　the　25　ppb　OH-PCBs　was　adsorbed,　the　average　pore　size　of　the　MIPs　decreased　from　1.4614　nm　to　1.3964　nm,　and　the　pore　volume　decreased　from　0.001928　cm3/g　to　0.001697　cm3/g.　As　a　result,　the　total　time　needed　for　the　complete　outflow　of　a　certain　amount　of　water　increased　accordingly.　The　total　time　had　a　relationship　with　OH-PCBs　concentration　in　the　range　of　1.0　to　100　ppb,　and　the　detection　limit　was　as　low　as　0.3　ppb.　The　proposed　technique　has　been　successfully　applied　for　the　detection　of　4　＇-OH-PCB　30　in　the　environmental　samples.　The　detection　of　different　targets　could　be　easily　achieved　by　simply　changing　MIPs　of　different　imprints.