Abstract: ob＜x＞jective Ki-67 is a reliable marker to indicate the proliferative activity of tumor cells. In this study, we explore Ki-67 ex＜x＞pression and its prognostic significance in histological subtypes of lung adenocarcinoma (LUAD). Methods We retrospectively analyzed 171 LUAD patients who underwent surgery treatment between January 2018 and December 2020 in our department. The Ki-67 ex＜x＞pression was detected by immunehistocheistry. Associations between Ki-67 ex＜x＞pression and histological subtypes of LUAD, as well as other clinicopathological characteristics, prognosis of patients were evaluated. Results Ki-67 ex＜x＞pression differed across LUAD histological subtypes. The lepidic predominant adenocarcinoma had the lowest ex＜x＞pression level of Ki-67 15%（5%-20%）, followed by acinar 15%（10%-30%）, papillary 10%（7.5%-35%）, micropapillary 25%（10%-67.5%），and solid predominant adenocarcinoma 30%（25%-50%)（P=0.0001). Tumors with solid or micropapillary components also had a higher Ki-67 ex＜x＞pression than those without solid or micropapillary components（P<0.0001）. Lepidic components was associated with lower Ki-67 ex＜x＞pression （P<0.05). Besides, the ex＜x＞pression of Ki-67 was higher in males, smokers, patients with larger tumor size, lymph node me＜x＞tastasis, pleural lymphatic vessels invasion, higher TNM stage and solid nodule. Logistic regression analysis showed that patient’s gender, histological subtypes, diameter of tumor were influencing factors of high ex＜x＞pression of Ki-67. KM survival analysis showed that increased Ki-67 ex＜x＞pression was significantly associated with inferior disease-free survival（χ2=7.598，P =0.006）. Conclusion The ex＜x＞pression of Ki-67 is related to histological subtypes of LUAD. High ex＜x＞pression of Ki-67 in LUAD is associated with poor prognosis.