In this paper, uncertainties in determining the offshore wind and wave energies were considered to estimate the wind and wave energy potentials in the southern Caspian Sea. For this purpose, 11 years of ECMWF data in 210 points were collected in the study area for the analysis. First, a SWAN model for wave modeling was performed and then, the wave and wind energies were calculated using conventional analysis. Next, the uncertainties in air density, wind speed, wind speed distribution parameters, wind turbine power performance, peak wave period, significant wave height in each peak wave period, and wave energy converter were considered and a Monte Carlo simulation for 1000 years was conducted for uncertainty analysis. Results showed that uncertainty analysis results in almost 9% lower average wave power density and 7.3% less exploitable energy than conventional analysis. In addition, wind power density computed by uncertainty analysis was on average about 4% higher than that obtained with the conventional analysis; however, the exploitable wind energy resulting from uncertainty analysis was 3% lower than the values computed by conventional analysis.