Small intestinal metastasis from lung cancer is a relatively rare occurrence, and often causes intestinal obstruction, gastrointestinal perforation, and/or gastrointestinal bleeding making it is an oncological emergency. Many patients have been reported to undergo emergency surgery owing to the rapid progression of the intestinal metastatic lesion; however, information regarding the changes that occur in such metastases over time remains lacking. Therefore, we analyzed 4 patients who had small intestinal metastases arising from lung cancer, who were treated during a 10-year period (January 2011 to December 2020), and whose tumor diameter changes were recorded. The average tumor volume growth rate was 1.48 (1.31-1.78) -fold, and the median observation period was 22 (4-39) days, showing a rapid increase. Histopathologically, in patients with a high degree of primary tumor atypia, rapid tumor growth caused by intratumoral hemorrhage may occur. This was considered to be one of the factors responsible for the rapid increase in tumor volume.