Eutrophication analyses of two subtropical storage reservoirs in Macau, the Special Administrative Region of China, namely Main Storage Reservoir (MSR) and Sai Pa Van Reservoir (SPVR), were performed in this study. Totally, 17 monthly water parameters including, five hydrological parameters (precipitation, imported volume, exported volume, water level, and hydraulic retention time), four physical parameters (temperature, pH, turbidity, and conductivity), seven chemical parameters (dissolved oxygen, Ammonium, nitrite, nitrate, total nitrogen (TN), orthophosphate (PO), and total phosphorus (TP)), and one biological parameter (phytoplankton abundance) were sampled and monitored in 2010. The correlation analysis and principle component regression (PCR), that is, principle component analysis (PCA) followed by multiple linear regression (MLR), were used to simplify the complexity of the relationships and to predict the phytoplankton abundance levels as well. The eutrophication analyses results showed that both reservoirs were in eutrophic status with the trophic state indices of 58-72 for MSR and 51-71 for SPVR, respectively. Phytoplankton abundance in both reservoirs were found to be linearly correlated with turbidity, temperature, and TP, while anti-correlated with conductivity, TN, nitrate, TN/TP, and water level. The PCA showed that three PCs with Eigen value over one, can explain 84.6% of total variation of the water parameters in MSR, while only two PCs can explain 70.8% for SPVR. The MLR models can be used for predicting phytoplankton abundance in the reservoirs with the predictive power of 0.90 in MSR, while only of 0.67 in SPVR.