ObjectiveTo study the expressions of BRAF gene in papillary thyroid microcarcinoma (PTMC) and papillary thyroid carcinoma (PTC) >1 cm in diameter, and the invasiveness of PTMC and PTC. MethodsThe data of 275 patients with PTC received surgical treatment and with BRAF gene mutation results in West China Hospital of Sichuan University from 2011 September to 2013 September were retrospectively analyzed. According to the size of tumors, the patients were divided into three groups, was the diameter <1 cm group, 1 cm< diameter≤2 cm group, and diameter >2 cm group,respectively. The ratio of BRAF gene mutation, and the degree of risk of extrathyroidal invasion and lymph node metastasis were compared. ResultsUnivariate analysis showed that tumor size was not related with the age, gender, and BRAF gene mutation rate (P>0.05), while the tumor size was related with the extrathyroidal invasion and lymph node metastasis (P<0.05), and the ratio of BRAF gene mutation was related with the extrathyroidal invasion and lymph node metastasis (P<0.05). Multivariate analysis showed that tumor size was associated with extrathyroidal extension (P=0.009) and lymph node metastasis (P=0.000). ConclusionsBRAF gene mutation can increase the extrathyroidal invasion and lymph node metastasis risk of PTC, and it is no significantly correlated with tumor size of PTC. The invasiveness of PTC increases with the increased of tumor size, but the PTMC of BRAF gene mutation positive is still require positive treatment.