Wettability is one of the key controlling parameters for multiphase flow in porous media and significant for various geoscience applications such as geological storage of CO2, EOR, and energy storage. In this study, by the means of high-resolution imaging, a series of displacement experiments of brine invasion into oil-saturated microfluidic cells under various wettability conditions were conducted to investigate the wettability effects on displacement stability and fluid distributions. Displacements were studied using two oil fluid systems with M (the ratio of the viscosity of the defending fluid to that of the invading fluid) to be 0.85 and 100 respectively under three different flow rates (capillary number Ca ranging from 9.21 × 10−8 to 9.21 × 10−6). Then quantitative analysis of displacement patterns based on fluid distributions images under different flow conditions are performed. Remaining oil distributions are investigated and correlated with capillary forces and wettability conditions. By symmetrically varying the wettability of the flow cell to three different wettability conditions (water-wet, intermediate-wet and oil-wet), we found that as the viscous ratio (M)=0.85, at low capillary number 9.21 × 10−8 when capillary force is dominated, the displacement becomes more efficient as the flow cell becomes more hydrophobic. At small capillary number, residual oil saturation is decreased from 66.89% for water-wet to 59.22% for intermediate-wet and 50.45% for oil -wet. With the capillary number increased to 9.21 × 10−6 , the displacement pattern becomes more compact with 50.62% residual oil saturation. It is noted that with wettability altered from water-wet to oil-wet under the capillary number of 9.21 × 10−7, crossover occurs from stable flow into capillary-dominated flow displacement, resulting in lower displacement efficiency and lager residual oil saturation (Sor=59.77%). When the viscous ratio was increased from 0.85 to 100, the viscous fingering is found to be more obvious, resulting in lower the displacement efficiency as the viscous force dominates the displacement for all the flow conditions compared with fluid flows under M=0.85. Moreover, when the viscous force is increased by increasing flow rates, wettability effect on displacement efficiency and residual oil saturation is suppressed.