One of the most common tumor is thyroid cancer many factors contributed to this cancer one of them is cyclin dependent kinases 1 (CDKs1) which paly a role in regulation of cell cycle. The study was aimed to evaluate the expression of CDK1 in thyroid carcinoma by immunohistochemical technique .There were 100 individuals enrolled in this study divided into two groups : patients with thyroid cancer 50 (20 benign thyroid cancer , 30 malignant thyroid cancer) and 50 controls as second group from October 2021 till April 2022 at Imam Hussein medical city Karbala Iraq. The thyroid tissue sample of all individual were undergone for immune histo chemistry test for CDK1. The result was showing significant difference (P value ˂ 0.00001 ) in expression of CDK1 between benign and malignant thyroid cancer their expression in benign cases 8(40%), for malignant cases 14(46.1%) { (10 (33.33%) classical type and 4(13.33%) follicular type }only 9 (30%) while only 1% of benign cases were strong staining. All apparently healthy thyroid tissue was negative for expression of CDK1. The study was concluded that Cyclin D1 overexpressed in Papillary thyroid carcinoma in comparison with follicular adenoma