The aims of the study were to identify a subpopulation more likely to be at greater risk of recurrence in small T1b-c node-negative hormone receptor (HR)-positive breast cancer, and which would benefit from adjuvant chemotherapy. Clinico-pathologic characteristics and clinical outcomes of 538 postoperative HR-positive T1b-cN0 breast cancer patients were retrospectively analyzed. High Ki67 index and a young age (< 35 years) were identified as independent risk factors for relapse (p < 0.0001 and 0.015, respectively). A nomogram based on Cox-regression model showed an area under the curve (AUC) of 0.73 in the training set. The validation set showed a good discrimination with an AUC of 0.65. In patients with high nomogram scores (≥ 100, n = 24, 4.5%) who had high Ki67 index with more than 75%, or young age (< 35 years) and a Ki67 index > 50%, the relapse-free survival curve of patients who had received anthracycline-containing adjuvant chemotherapy showed a better outcome than those who had not (p = 0.029). Ki67 index and age are valuable surrogate markers to predict recurrence and as indicators of tumors that could benefit from adjuvant chemotherapy in small T1b-c node-negative HR-positive breast cancer.