Old age alone does not reflect an intolerability to chemotherapy. However, upfront dose reduction (UDR) of the first cycle of first-line palliative chemotherapy has sometimes been chosen by physicians for older adults with metastatic cancer due to concerns regarding adverse events. The development of predictive factors for UDR of palliative chemotherapy would be helpful for treatment planning among older adults. This was a secondary analysis of a study on predicting adverse events of first-line palliative chemotherapy in 296 patients (≥70 years) with solid cancer. We assessed the prevalence of UDR of the first cycle of first-line chemotherapy and the association of UDR with the variables of geriatric assessment (GA) and chemotherapy compliance. Among the 296 patients, 177 (59.8%) patients were treated with UDR. The mean percentage of UDR for the total patient group was 19.2% (range: 4–47%) of the standard dose. In a multivariate analysis, poor performance status (PS) and living without a spouse were independent predictive factors of UDR of first-line palliative chemotherapy in older adults. Patients with UDR showed fewer grade 3–5 adverse events versus the standard dose group. Study completion as planned was significantly higher in the UDR group versus the standard dose group. Older adults with UDR better tolerated chemotherapy than patients with a standard dose.