Abstract: Linking the largest carbon pools, rivers play an essential role in global carbon cycle. Evaluating the horizontal flux of various carbon fractions, carbon dioxide emission and their proportion in the Minjiang River is important for understanding the regional carbon cycle. The monthly water sampling was conducted at Zhuqi hydrographic station in the lower reach of the Minjiang River from November 2013 to October 2014. The contents of the DIC (dissolved inorganic carbon), DOC (dissolved organic carbon) and POC (particulate organic carbon) were determined and the horizontal/vertical fluxes of carbon fractions were estimated with relevant parameters. The results indicated that the ranges of c(DIC), c(DOC) and c(POC) were 230-892, 112-209 and 14-183 μmol/L, respectively. The annual carbon horizontal flux of the Minjiang River was 46×10¹⁰ g/a, 63% of which was DIC, serving as the main component. Meanwhile, DOC horizontal flux was 11×10¹⁰ g/a and POC horizontal flux was 6×10¹⁰ g/a, equivalent to 55% that of DOC. The dissolved carbon represented the majority of all fractions. Moreover, seasonal variabilities of carbon fractions were different. The DIC concentration decreased in wet season while increased during dry season, which indicated that DIC output was restricted by the supply of watershed ecosystem. The DOC concentration was largely invariable in contrast to the runoff variation and the POC concentration correlated positively with the discharge amounts. The DIC horizontal flux was evenly distributed throughout the year while organic carbon flux peaked in the wet season. The partial pressure of CO₂ on river surface ranged from 1, 500 to 6, 400 μatm (1 atm=101, 325 Pa). Thus, lower reach of the Minjiang River was CO₂ source of the atmosphere. The estimated CO₂ vertical flux amounted to only 2% of DIC horizontal flux, which was the major components of the DIC efflux for the Minjiang River.