Abstract: Gastric cancer (GC) is a serious worldwide health burden as well as its treatments especially chemotherapy result in many bothersome physical adverse effects and psychosocial problems, which negatively impact patients' quality of life (QoL). Effective self-care education about chemotherapy's adverse effects aids patients in better managing them, adapting to chemotherapy, and improving treatment outcomes. Furthermore, boosting cancer patients' confidence about their ability on performing self-care strategies could have a significant impact in enhancing their functioning role and quality of life. Study aim: evaluate the effectiveness of self-care practices education program on enhancing chemotherapy adverse effects and quality of life for patients with gastric cancer. Study Design: a quasi-experimental design. Setting: Oncology and chemotherapy outpatient clinic at Zagazig University Hospitals, Al Sharkia governorate, Egypt. Subject: A Purposive sample of 50 adult patients with GC receiving chemotherapy. Tools: Interview questionnaire, Self-reported chemotherapy adverse effects questionnaire, Self-care practices questionnaire, and EORTC QLQ-C30 questionnaire to measure patients' QoL. Results: the highest percentage of studied patients (54%, 56%, 56%, 36.0%, and 52%) were <50 years old, males, from urban, had mid qualification and smokers respectively. There was a statistically significant difference and improvement in patients' total knowledge, chemotherapy adverse effects, self-care practices toward these adverse effects, and quality of life at the post-intervention phase of the program as compared to the pre-intervention phase (p=0.0001). Patients' knowledge and self-care practices improvement correlated positively with QoL and negatively with chemotherapy adverse effects that correlated negatively with QoL. Conclusions: Self-care practices education program had an effective role in improving knowledge and self-care practices of patients with GC toward chemotherapy adverse-effects, which resulted in decreasing these adverse-effects and enhancing their quality of life. Recommendations: Availability of Self-care practices education programs and guidebooks in all Egyptian Oncology Centers for patients with GC is recommended to inform them about chemotherapy adverse effects and self-care strategies to handle it in a specific and comprehensive manner. Keywords: Self-care practices, Education program, Chemotherapy adverse effects, Quality of life, Gastric cancer.