This study aims to evaluate changes in quality of life of cancer patients at the beginning of the first and the second cycle of chemotherapy (CT) in hospitals in Belo Horizonte, Minas Gerais State, Brazil. Longitudinal, prospective, descriptive study with a quantitative approach. We enrolled 230 patients, from a broader cohort, diagnosed with the five most frequent types of cancer (breast, colorectal, cervical, lung, and head and neck), aged 18 years or older, who were initiating CT for the first time. quality of life was assessed with the EORTC QLQ-C30 version 3, applied at the beginning of the first and second chemotherapy cycle. The paired Wilcoxon test was used to identify differences in quality of life between the two time points. A multivariate linear regression analysis was performed using the bootstrap method to investigate potential predictors of global health Status/quality of life. There was a significant increase in patients' emotional function scores (p < 0.001) as well as symptom scores for pain (p = 0.026), diarrhea (p = 0.018), and nausea/vomiting (p < 0.001) after initiation of CT. Widowhood was associated with improvements in the global health Status/quality of life (p = 0.028), whereas the presence of cervical cancer (p = 0.034) and being underweight (p = 0.033) were related to poorer global health status/quality of life scores. CT has detrimental effects on patients' physical health but, on the other hand, it leads to improvements in the emotional domain. Patients' individual characteristics at the beginning of CT are associated with changes in their quality of life. Our study could help identify these characteristics.