Abstract: The distribution of Chl a concentration in riverine and coastal surface waters of the Laizhou Bay was investigated in September 2012. Related environmental parameters were also measured and their impact on the distribution of Chl a concentration was analyzed. The results showed that the average concentration of Chl a in the riverine and marine regions was 51.9 and 3.9 g/L, respectively. In the riverine region of the Laizhou Bay, only suspended particulate matter (SPM) had a significantly positive correlation with Chl a; while in the marine region, SPM, PO4-P, NH4-N and NO3-N had significantly positive correlations with Chl a. Both nitrogen (N) and phosphorus (P) were the limiting factors for the distribution of Chl a in the surface waters of the marine region, and N seemed to play a greater role than P. Surface waters in the riverine region were mainly in the status of serious and high eutrophication, and surface waters in the marine region were mainly in the status of low eutrophication. The rivers, the waters of which contain nutrients of high concentration, discharge considerable amounts of nutrients into the Laizhou Bay, making its coastal marine area more suitable for the growth of phytoplankton and then promoting the concentration of Chl a, and have the potential to aggravate the extent of eutrophication of this area.