To estimate the status of β-cell dysfunction and insulin resistance of breast cancer (BC) patient without history of diabetes mellitus (DM) after systemic treatment through an oral glucose tolerance test (OGTT) and insulin releasing test (IRT). All the 128 BC patients without history of DM after systemic treatment underwent OGTT and IRT test. Fasting and 2-h glucose levels were measured to confirm undiagnosed DM and prediabetes. Insulin sensitivity was estimated by homeostasis model assessment of insulin resistance (HOMA-IR) and Matsuda index and disposition index (IGI/HOMA-IR). Insulin secretion was estimated by the insulinogenic index (IGI) [Δ insulin/Δ glucose (30-0 min)]. Insulin concentrations during the OGTT and IRT at baseline were used to derive the patterns of insulin secretion curve (pattern 1, pattern 2, pattern 3, pattern 4 and pattern 5), which were used to estimate the risk of developing DM. Of 128 BC patients without history of DM after systemic treatment, there were 46 cases (35.9%) of NGT, 60 cases (46.9%) of prediabetes and 22 cases (17.2%) of DM. The BMI of prediabetes and DM were higher than NGT groups with statistical significance. After adjusted for BMI, IGI was significantly lower in DM group but not significantly different between NGT group and prediabetes group. HOMA-IR, Matsuda index and disposition index were significantly different in DM group compared with NGT group and prediabetes and also significantly different between NGT and prediabetes groups. The total rates of patterns 4 and 5 in NGT and prediabetes groups were 15.3% (10.9 and 4.4%) and 48.3% (31.6 and 16.7%), respectively. β-Cell dysfunction and insulin resistance may appear in BC patients after systemic treatment. BC patients have high risk in development of DM even in NGT and prediabetes groups confirmed by OGTT.