Objective To evaluate and screen out the specific characters of thyroid nodules on grayscale and color Doppler ultrasonography. Methods One hundred and four thyroid nodules in 95 patients were studied with gray-scale and color Doppler ultrasound before surgery.According to the probability of malignancy,the main independent characters were screened out by Logistic regression analysis and then got the formula which could calculate the probability of malignancy.Results Fifty three nodules,included 44 hyperplasia,7 adenomas,1 switch granuloma and 1 Hashimoto's disease,were benign.Fifty one nodules,included 47 papillary carcinomas,3 medullary carcinomas,1 metastatic carcinomas,were malignant pathologically.The significant characters to differentiate malignant from benign were the shape,margin,border,halo,echostucture,echogenecity,echo uniformity,calcicum,bolood vessel shape and partial abnormal rich blood of thyroid nodules.After two variables logistic regression analysis,a fomula were worked out.Probability of malignancy=1/1+e-z,which z=-7.44+1.30×halo+1.05×calcicum+1.5×vessel shape.If a thyroid nodule with no halo,microcalcicum and irregular vessel shape,the probability of malignancy was 0.99,while with complete halo,no calcicum and regular vessele shape,the probability of malignancy of the nodule was 0.02.Conclusions The halo,calcium and blood vessel shape of thyroid nodules were three independent characters of thyroid nodules to predict malignant thyroid nodules on gray scale and color Doppler ultrasound.