Objective To observe the effects of interventional therapy on the thyroid tumor by intratumoral injection of 32Phosphorus-radiocolloid (32P-colloidal) under ultrasonic guidance. Methods Patients with thyroid tumors who underwent intratumoral injection of 32P-colloidal (32P-colloidal group, n=30) and pure ethanol (control group, n=30) under ultrasound guidance were selected. The therapeutic effect and adverse reactions were recorded by follow-up after being treated for 2, 4, 6, and 8 months. Results Regular follow-up showed that the therapeutic effect of 32P-colloidal group was correlated with the tumor size after being treated for 6 and 8 months (P=0.042 and 0.019, respectively). The therapeutic effect of 32P-colloidal group was significantly better than that of the control group after being treated for 8 months (P=0.011). The main adverse reactions of 32P-colloidal group were mild pain at tumors sites (33.00%), local skin erubescence (16.67%), and radiodermatitis (6.70%). Conclusion The interventional therapy of thyroid tumor by intratumoral injection of 32P-colloidal under ultrasonic guidance is convenient and effective with less adverse reactions. The therapeutic effect is correlated with the tumor size.