In this study, Clarias gariepinus heads were used as the raw material to prepare fish head broth. The ultrasonic pretreatment process was optimized by the combined use of one-factor-at-a-time method and response surface methodology. The temperature during ultrasonic treatment, ultrasonic power and time were considered as the independent variables, and water-soluble protein content was the only dependent variable. The results showed that the optimal process conditions were found to be ultrasonication at 35 ℃ and 490 W for 31 min. Under the optimized conditions, the experimental content of water-soluble protein in fish head soup, (0.78 ± 0.01) g/100 mL, was close to the model predicted value, confirming the practical applicability of the proposed model.