Topsoil soil organic carbon (SOC) data were collected from long-term Chinese agro-ecosystem experiments presented in 76 reports with measurements over 1977 and 2006. The data set comprised 481 observations (135 rice paddies and 346 dry croplands) of SOC under different fertilization schemes at 70 experimental sites (28 rice paddies and 42 dry croplands). The data set covered 16 dominant soil types found in croplands across 23 provinces of mainland China. The fertilization schemes were grouped into six categories: N (inorganic nitrogen fertilizer only), NP (compound inorganic nitrogen and phosphorus fertilizers), NPK (compound inorganic nitrogen, phosphorus and potassium fertilizers), O (organic fertilizers only), OF (combined inorganic/organic fertilization) and Others (other unbalanced fertilizations such as P only, K only, P plus K and N plus K). Relative change in SOC content was analyzed, and rice paddies and dry croplands soils were compared. There was an overall temporal increase in topsoil SOC content, and relative annual change (RAC, g kg(-1) yr(-1)) ranged -0.14-0.60 (0.13 on average) for dry cropland soils and -0.12-0.70 (0.19 on average) for rice paddies. SOC content increase was higher in rice paddies than in dry croplands. SOC increased across experimental sites, but was higher under organic fertilization and combined organic/inorganic fertilizations than chemical fertilizations. SOC increase was higher under balanced chemical fertilizations with compound N, P and K fertilizers than unbalanced fertilizations such as N only, N plus P, and N plus K. The effects of specific rational fertilizations on SOC increase persisted for 15 years in dry croplands and 20 years in rice paddies, although RAC values decreased generally as the experiment duration increased. Therefore, the extension of rational fertilization in China's croplands may offer a technical option to enhance C sequestration potential and to sustain long-term crop productivity.