Objective: There is an increasing interest in human epidermal growth factor receptor 2 (HER2) low expression breast cancer with the result of novel anti-HER2 antibody-drug conjugates for breast cancer. HER2 low expression breast cancer is expected to become a new type of breast cancer. This study analyzed and compared the clinicopathological features and survival data of breast cancer with HER2 low expression group [immunohistochemistry (IHC) 1+ or IHC 2+, and fluorescence in situ hybridization (FISH) negative] and HER2 zero expression group (IHC 0), in order to explore the difference in clinical biology of HER2 low expression breast cancers. Methods: Among 1 250 female patients with primary non-metastatic breast cancer admitted to the Breast Disease Center of Peking University First Hospital from January 2014 to December 2017, 969 cases were HER2 negative (IHC 0, 1+, 2+, and FISH was not amplified). The clinicopathologic features and prognosis of the patients with HER2 low expression (IHC 1+ or 2+, and unamplified by FISH) and HER2 zero expression (IHC 0) were analyzed. Disease free survival (DFS) and overall survival (OS) were evaluated, survival rates were calculated by Kaplan-Meier curve, and survival differences were compared by Log-rank test. Cox regression analysis of univariate and multivariate prognostic factors. Bilateral test was used, and P < 0.05 was considered statistically significant. Results: In the 969 patients with HER2 negative breast cancer, 606 had HER2 low expression (62.54%) and 363 had HER2 zero expression (37.46%). Compared with breast cancer with HER2 zero expression, those with HER2 low expression had higher N stage (P=0.001) and TNM stage (P=0.044), the proportion of non-specific histological types was higher (82.7% vs. 79.1%, P=0.009), the histological grade was higher (P=0.048), and the positive rate of hormone receptor was higher (83.2% vs. 75.2%, P=0.003). The percentage of Ki-67 value index >30% was lower (30.4% vs. 36.6%, P=0.044). There was no significant difference in DFS and OS between the two groups (P>0.05). In the 969 cases, 777 were hormone receptor positive and 192 were hormone receptor negative (triple negative cancer). Among the 777 cases with hormone receptor positive, 504 (64.9%) were HER2 low expression, and 273 (35.1%) were HER2 zero expression. Compared with breast cancer with HER2 zero expression group, the HER2 low expression group had a younger age (P=0.016), a higher proportion of premenopausal patients (P=0.029), more lymph node involvement (P=0.002), and a higher total TNM stage (P=0.031), and less frequent histological types of lobular and mucinous carcinoma (3.6% vs. 7.3%, 4.8% vs. 10.6%, P=0.001). There was no difference in DFS and OS between HER2 low expression and zero expression (P>0.05). Among 192 patients with hormone receptor negative, there were 102 cases (53.1%) with HER2 low expression and 90 cases (46.9%) with HER2 zero expression. Compared with the HER2 zero expression groups, HER2 low expression group was older (P=0.001), the proportion of premenopausal patients was low (P=0.029), the histological grade was lower (P < 0.001), the Ki-67 value index was lower (P < 0.001), and androgen receptor positive rate was higher (58.8% vs. 34.4%, P < 0.001). DFS was better than HER2 zero expression group (P=0.038), but there was no difference in OS between the two groups (P>0.05). Conclusion: HER2 low expression breast cancer accounts for about half of all breast cancers, and the incidence is much higher than that of HER2 positive breast cancer. Its clinicopathologic features are heterogeneous, and the status of hormone receptor expression has an impact on the clinical biology of this group.