Purpose: The study aimed to investigate the association between perceived social support and psychosocial adjustment of geriatric cancer patients undergoing chemotherapy. Methods: Two hundred geriatric patients provided consent were interviewed and the data collected using the Psychosocial Adjustment to Illness Scale (PAIS), the Multidimensional Scale of Perceived Social Support (MSPSS), In addition to demographic and clinical data. Data was collected from Kasr Al-Aini Center for Oncology and Nuclear Medicine, Cairo, Egypt after the study protocol was approved (Approval No. 10), August 2019. Correlations using Pearson and Spearman coefficients as well as binary logistic regression were used using The IBM SPSS software package, version 26. Results: The psychological distress domain was found to have the highest mean score (14.2±4.5) among the psychosocial adjustment domains, whereas extended family relations were found to have the lowest mean score 6.8 ± 2.09. The study also found that there was a significant negative correlation between the overall scores of the psychosocial adjustment scale and the multidimensional scale of perceived social support (p <0.001). Moreover, a significant negative correlation between the overall scores of the Multidimensional Scale of Perceived Social Support and the following sub- domains of the Psychosocial Adjustment Scale: health care orientation, extended family relations, and psychological distress (p <0.001) was detected. Those with high level of perceived social support were 0.044 times more likely to have high psychosocial adjustment compared to those with low level of perceived social support (p<0.001). Females were twice less likely to have high psychosocial adjustments compared to the males. Conclusion: Our findings indicate that there is an association between perceived social support and elderly' psychosocial adjustment. In addition, perceived social support is found to be an independent predictor of psychosocial adjustment. Therefore, establishing or strengthening the existing social structures throughout the treatment journey is recommended for elderly cancer patients.