Objective: Ki-67 plays an important function in cell division, but its exact role is still unknown. Moreover, few works regarding its overall function were published. The present study evaluated the clinical significance of Ki-67 index as a prognostic marker and predictor of recurrence in different molecular subtypes of breast cancer. The relationship of Ki-67 index with different clinicopathological factors was also analyzed.Methods: Ki-67 index was measured in 107 cases of primary breast cancer from 2010-2012. These patients were evaluated for estrogen receptor, progesterone receptor, and HER2. Ki-67 was divided according to percentage levels: < 15% and > 15%. Followup ranged from 32 months up to 6 years.Results: Approximately 44, 23, 15, and 25 cases were grouped as luminal A, luminal B, HER2 subtype, and triple-negative(TN),respectively. No luminal A patients showed Ki-67 level higher than 15%, and their recurrence was 20%. In luminal B group, Ki-67 level higher than 15% was observed in 69% of patients, and recurrence was 39%. In HER2 subtype, Ki-67 was higher than 15% in34% of cases, and recurrence was 40%. In triple-negative cases, Ki-67 was higher than 15% in 60% of cases, and recurrence was detected in 32% of patients. Patients with Ki-67 less than 15% displayed better overall survival than those with Ki-67 higher than15%(P = 0.01). Patients with Ki-67 higher than 15% exhibited higher incidence of metastasis and recurrence than those with Ki-67 less than 15%(P = 0.000).Conclusions: Ki-67 may be considered as a valuable biomarker in breast cancer patients. The present study as the overall function was published. The present study as the clinical significance of Ki-67 index as a prognostic marker and predictor The recurrence of different molecular subtypes of breast cancer. The relationship of Ki-67 index with different clinicopathological factors was also analyzed. Methods: Ki-67 index was measured in 107 cases of primary breast cancer from 2010-2012. These patients were evaluated for Estrogen receptor, progesterone receptor, and HER2. Ki-67 was divided according to percentage levels: <15% and> 15%. Followup ranged from 32 months up to 6 years. Results: Approximately 44, 23, 15, and 25 cases were Luminal B, HER2 subtype, and triple-negative (TN), respectively. No luminal A patients showed Ki-67 level higher than 15%, and their recurrence was 20%. In luminal B group, Ki-67 level higher than 15% was observ Ki-67 was higher than 15% in 34% of cases, and recurrence was 40%. In triple-negative cases, Ki-67 was higher than 15% Patients with Ki-67 less than 15% showed better overall survival of those with Ki-67 more than 15% (P = 0.01). Patients with Ki-67 higher than 15% than 15% exhibited higher incidence of metastasis and recurrence than those with Ki-67 less than 15% (P = 0.000) .Conclusions: Ki-67 may be considered as a valuable biomarker in breast cancer patients.