Seventeen species of chaetognaths belonging to nine genera and three families were recognized from the samples collected in estuaries of Tamshui River and Kaoping River from February 2003 to November 2003. In Tamshui River estuary, eleven species belonging to eight genera and three families were recorded, with the mean abundance of 807 ¡Ó 1154 ind./100m3, while in Kaoping River estuary, fourteen species belonging to nine genera and three families were identified, with the mean abundance of 1601 ¡Ó 2796 ind./100m3. The three most dominant species in both estuaries were Flaccisagitta enflata, Aidanosagitta crassa and A. neglecta, and together they comprised ¡Ö95¢Mof the total chaetognaths. The abundance of chaetognaths showed apparent seasonal changes, higher abundance in February in Tamshui River estuary and in May in Kaoping River estuary. The abundance of chaetognaths showed no significant correlation with temperature in both estuaries, but displayed higher relationships to salinity and copepods. The body length¡]BL¡^ of Flaccisagitta enflata showed significant seasonal and spatial differences, with larger in both February and May in Tamshui River estuary but only in May in Kaoping River estuary. Aidanosagitta crassa showed significantly larger in BL in February than in other months in Tamshui River estuary, but it was not in Kaoping River estuary. The stage I of chaetognaths dominated in this study area and occupied ¡Ö80¢Mof the total count. Other stages mostly presented in February in Tamshui River estuary and in May in Kaoping River estuary. Only Fl. enflata was found to have gut content, all copepods, in February and May. The estimated daily predation impact on the standing stock of copepods ( by number ) was insignificant, only ¡Õ1¢H in both estuaries.