Since 2019, many studies on COVID-19, which has caused extensive damage as a pandemic, have been ongoing worldwide. These include serological and biochemical studies using sera from patients and animal models. Testing with these sera must be performed after the inactivation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Heat treatment, UV irradiation, and/or gamma-ray irradiation are used to inactivate viruses in serum. Determining the inactivation conditions that ensure the inactivation of viruses and minimize the effect on test results after inactivation is important to ensure worker safety and accuracy of test results. In this study, serum samples containing SARS-CoV-2 were subjected to heat, UV irradiation, and gamma irradiation to determine their inactivation conditions. The viral titers were below the detection limit after heating at 56°C for 1 h or 60°C for 15 min, UV-B irradiation with a transilluminator for 30 min, or gamma ray irradiation with ⁶⁰Co at 10 kGy. These results provide useful information for safe serological and biochemical experiments.