Background: In 2012, worldwide there were 1.7 million new cases of breast cancer. Knowledge of HER-2 and tumor size can be used as the best indicator of prognostic factors and treatment of breast cancer. The function of the HER-2 strongly associated in the setting of tumor size growth. When there is overexpression of HER-2 will lead to growth in the size of the tumor had become unmanageable. This study was conducted to determine the comparation between HER-2 with the size of tumors in breast cancer patients. Aim: To determine the comparation between overexpression of HER-2 with tumor size in patients with breast cancer. Methods: Cross sectional study was carried out against 72 Patients with a diagnosis of breast cancer that has been conducted immunohistochemical examination (oncoprotein HER-2/neu) and histopathological (tumor size). Sampling research from January to December 2015. Data were analyzed by Chi- Square test done gradually include univariate and bivariate analysis. Results: From 72 samples obtained from the study of patients with tumor size ≤5 cm and> 5cm by 47 (65.3%) and 25 (34.7%) patients. In size ≤2 cm and> 2 cm by 24 (33.3%) and 48 (66.7%) patients, while the expression HER-2 positive in 26 (36.1%) patients and HER-2 negative with 46 (63.9%). By using the Chi-square test of correlation values obtained P = 0.119 for the size tumor ≤5 cm and> 5cm and P = 0.489 for tumor size ≤2 cm and> 2 cm for the comparation between the size of the tumor with overexpression of HER-2. Conclusion: No comparation was statistically significant overexpression of HER- 2 with large tumor size in patients with breast cancer.