Nutritional status tends to be poor in patients undergoing chemotherapy. We investigated anorexia caused by olfactory dysfunction by examining olfactory sense in chemotherapy patients and healthy volunteers. We used the Open Essence® olfactometry test, which assesses the accuracy of identifying 12 different odors. Twenty-seven patients (mean age 69.8 years) who received chemotherapy for lung cancer from March 2016 to September 2017 participated in multiple olfactometry examinations from the start of their chemotherapy. We also examined 284 healthy volunteers (mean age 41.9 years), and performed an additional subgroup analysis with 35 volunteers aged 60 years or older (mean age 73.2 years) to more closely align with the mean age of the patients. The mean accuracy rate was 44.4% for the patients, although this rate varied from odor to odor. In contrast, the mean accuracy rate of the healthy volunteers was 76.8%. There were significant differences according to sex and smoking history. For the subgroup of healthy volunteers aged 60 years and older, the mean accuracy rate was 54.5%; accuracy rate decreased as age increased. There was no significant difference in the accuracy rate according to type of chemotherapy, but the overall rate for patients was lower than that for healthy volunteers. Our results show that olfactory sense in lung cancer patients undergoing chemotherapy is altered compared with that in healthy individuals. Smoking habit was shown to have the greatest effect and most of the lung cancer patients in this study were smokers. A change in olfactory sense caused by smoking was also noted in the healthy volunteer group. We intend to conduct a similar investigation of patients with diseases other than lung cancer in the future as well as utilize the findings to investigate nutritional status.