Two kinds of hydrophilic conjugated polymer, poly[9,9-bis((6-N,N,N-trimethylammonium)hexyl)fluorine-alt-co-(1,4-benzo-{2,1',3}-thiadiazole] (PFBD) with cationic groups and poly[9,9-bis(4'-sulfonatobutyl)fluorine-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] sodium salt (PFSBT) with anionic groups, were prepared by Suzuki method. The as-prepared conjugated polymers were formed nanoparticles (NPs) with the diameter of 20 nm in water. Under a 488 nm laser excitation, the PFBD shows an emission peak at 560 nm and with the quantum yield of 26%, while the PFSBT shows an emission peak at 575 nm with the quantum yield of 4%. We investigated the cellular uptake and cell viability of two conjugated polymer NPs (CPNPs) on human gastric adenocarcinoma (SGC-7901). Both of CPNPs show low cytotoxicity by MTT assay, even at the concentration of 40 ppm. Flow cytometers studies indicate that the fluorescence intensity of PFBD NPs is stronger than that of PFSBT NPs. These results would provide a basic experiment evidence in the fluorescence imaging field.