The impact of the influences from the south on the oxygen minimum zone (OMZ) of the eastern tropical South Pacific (ETSP) is investigated with a high-resolution coupled physical-biogeochemical model. Model assessment of the most realistic model configuration suggests good agreement of horizontal and vertical oxygen and nutrient distributions with observations. Comparisons among model configurations with different southern boundary conditions indicate that the southern boundary is an important oxygen source to the OMZ in the ETSP, mainly influencing the southern and inshore sides. Lateral flux estimations show that our model domain is gaining oxygen, but losing nitrate and phosphate through the southern boundary. The southern boundary is found to have more significant influence on O2 concentration of the deep layer than of the upper layer, suggesting a pathway of deep northward intrusion of well-oxygenated southern waters. The Southern Ocean is thought to be sensitive to global warming due to reductions in deep convection, resulting in a significant decrease in O2 concentrations. As the southern boundary of ETSP is directly facing the Southern Ocean, this study could give some insights into the impacts of Southern Ocean variations on the oxygen and nutrient cycles of the ETSP.