This study was conducted to explore the trajectory of fatigue and related factors on people with lung cancer during chemotherapy. A total of 23 patients with lung cancer participated in the beginning stage of the study. However, 11 dropped out because of death or discontinuity of the studys regimens. The data using the Pipers Fatigue Scale, were collected twice the first day of each treatment cycle and the last day of the completion of 6 cycles. Also, the scores of fatigue using the Visual Analogue Scale (VAS) were measured on the same day of each week during chemotherapy to explain the trajectory of fatigue. The data obtained were analyzed using the Wilcoxon signed ranks tests and Kendalls tau b correlation coefficient. The score of fatigue increased in the first two weeks after the administration of chemotherapy, while decreasing after the second week. During the 1st, 5th, and 6th cycles, the scores of fatigue were greater than 5.5 out of 10. Overall, except for the 6th cycle, the score of fatigue was the highest in the first week. This could be accounted for there only being a small number of patients included in the 6th cycle. In conclusion, fatigue was severe at the end of the first week of chemotherapy, and then increased to reach a plateau in the fifth and sixth stages. The results of this study will help oncology nurses to understand the process of fatigue during chemotherapy. It will be useful to create various intervention programs to decrease fatigue in people with cancer especially in the first week of the chemotherapy.