In this study, the moisture sorption isotherm of fresh compost was experimentally determined using a modified gravimetric method. The experiments were conducted at a temperature of 50 °C with an airflow rate of approximately 28 m/h. The results indicated that the moisture sorption isotherm exhibited a type II S-shaped curve. Notably, capillary condensation became significant at relative humidity levels exceeding 75%. A nonlinear regression analysis was performed to fit fifteen moisture sorption isotherm models from the literature to the experimental data. The models were evaluated based on their statistical parameters, specifically R2, SSE, and RMSE. Among the models, the Smith model was identified as the most accurate for predicting the relationship between equilibrium moisture content and relative humidity. Additionally, the Halsey, Henderson, and Luikov models also demonstrated good fit.