Salalah Coastal Aquifer is considered as the main natural water resource that the entire city is depending on for agriculture, domestic and commercial use. The excessive groundwater pumping becomes a concern as seawater intrusion has been already reported at different farms and abstraction wells mainly close to coastal side of Salalah Plain. The main objective of this study was to setup, calibrate and validate a model for Salalah Coastal Aquifer that can be used to assess aquifer behaviour and seawater intrusion pattern. The study was conducted over 640 km2 of Salalah Plain which represent around 83% of Salalah Plain total area. Injection scheme, direct rainfall and dams were considered as sources for aquifer recharge while groundwater abstraction occurred through agricultural, domestic and commercial uses. The groundwater modeling was carried out using MODFLOW. The model was calibrated and validated at steady state and transient state using data from 2000 to 2019. It was used to define the aquifer properties such as hydraulic conductivity, specific yield, and vertical anisotropy. MODFLOW results were mapped to MT3DMS in order to simulate solute transport at [AS1]transient state. The longitudinal dispersivity and porosity of the aquifer were defined through the calibration and validation of the model. MODFLOW calibration and validation results showed good agreement between the field observed head values and model computed values with RMSE of 0.65. Across the three aquifer layers, the hydraulic conductivity was found between 10 m/day to 100 m/day, vertical anisotropy was found to be 4 and the specific yield was found between 0.01 to 0.1. MT3DMS calibration and validation results showed good agreement between the field observed TDS values and model computed values. The sensitivity analysis indicated that hydraulic head had more sensitivity to the hydraulic conductivity among the three calibrated parameters, while groundwater abstraction sensitivity was the highest among all the input parameters to the system. The calibrated values of the longitudinal dispersivity and porosity were found at the range of 500 m to50000 m, and 0.4 respectively. The study indicated a clear impact of seawater intrusion at coastal side of the Salalah Plain. The predictive modeling indicated an average of 1.5 m drop in hydraulic head across the whole study area by 2040, while seawater intrusion effect was expected to increase at the coastal side with potential extension to the central area if the Salalah plain. The study concluded that the generated model can be used as a prediction tool to study the aquifer behaviour at different scenarios, as part of integrated water resources management within Salalah city.