This　study　developed　a　portable　and　sensitive　biosensor　for　the　detection　of　telomerase　activity　extracted　from　HeLa　cells　by　monitoring　urease　regulated　pH　change.　In　the　presence　of　telomerase,　the　telomerase　substrate　(TS)　primer　was　elongated　by　adding　telomeric　repeats　(TTAGGG)(n)　firstly.　The　TS　primer　was　then　immobilized　onto　streptavidin　magnesphere　paramagnetic　particles　(PMPs).　The　elongated　repeat　unit　can　hybridize　with　biotinylated　complementary　DNA　(cDNA)　to　specifically　capture　biotinylated　urease　onto　PMPs.　After　magnetic　separation,　the　PMPs　complex　was　mixed　with　urea　solution.　As　urease　can　catalyze　the　hydrolysis　of　urea　into　ammonia　and　induce　pH　increasing　of　the　solution,　the　activity　of　telomerase　can　be　detected　by　pH-sensitive　dyes　or　by　a　portable　pH　meter　easily.　The　changed　pH　has　a　linear　relationship　with　the　logarithm　of　the　number　of　HeLa　cells　from　50　to　10,000　and　with　a　detection　limit　of　similar　to　20　HeLa　cells,　which　indicated　the　proposed　method　have　potential　application　in　telomerase-related　cancer　diagnosis.