Background: Local ablative treatments play an important role for patients who cannot be treated surgically. Radiofrequency ablation is a well-established alternative to surgical treatment of thyroid nodules, however it also has disadvantages. Microwave ablation (MWA) is a new minimally invasive treatment promising several improvements. The aim of this retrospective study was to evaluate the effects of microwave ablation on thyroid nodules by ^99mTc-pertechnetate and ^99mTc-MIBI scintigraphy. Materials and Methods: 30 patients with overall 40 nodules were treated. For the ablation of thyroid nodules, a microwave generator working with frequencies from 902 to 928 MHz was used. The ablation time ranged between 120 and  300 seconds per ablation zone. The target temperatures ranged between 60-80 °C. Pre- and post- interventional, the radionuclide uptake was determined using a thyroid specific scintillation camera. For 27 cold nodules ^99mTc-MIBI was used for evaluation; 13 indifferent nodules were measured with ^99mTc-pertechnetate. Results: The relative change of uptake was detected as a quotient of pre- and post- therapeutic uptake. The statistical analysis of scintigraphy data proved the efficacy of microwave ablation. ^99mTc-pertechnetate scintigraphy  showed an uptake reduction of 39% (range 9 to 85%). ^99mTc-MIBI imaging showed a median reduction of 40% (p<0.01) (range 7 to 100%). Conclusion: The determined results show the effectiveness of MWA as a treatment option for benign thyroid nodules. With functional scintigraphy a significant activity decrease could be detected in the ablation zone; hence a verification of affectivity was possible after a short period of time.