Introduction: Upper gastrointestinal cancers (UGIC) related malnutrition has been found to harm cancer prognosis and treatment outcomes. The study purposed to investigate the prevalence of malnutrition and associated factors in newly diagnosed upper gastrointestinal cancer patients before treatment. Material and Methods: A cross-sectional study included newly diagnosed UGIC patients from October 2020 to March 2022. Sociodemographic, clinical (type, stage, and comorbidities), functional [Eastern Cooperative Oncology Group (ECOG) Performance Status Scale], anthropometric measures [weight, height, the percentage of weight loss past 1-month], biochemical profiles [full blood count and albumin], total daily energy protein intake, and malnutrition level [Subjective Global Assessment (SGA)] were assessed. Results: The study recruited 409 participants, and 92.1% were malnourished. The mean for age, weight, percentage of weight loss past 1-month, total daily energy and protein intake, SGA score, and serum albumin of participants were 60.3±12.5years, 57.8±15.1kg, -8.2±6.0%, 17±5kcal/ kg/day, 0.7±0.1g/kg/day, 12.2±4.5 and 35.6±6.1g/L respectively. About 88% and 96% experienced vomiting and dysphasia, respectively; 51.3% was ECOG scale 2. According to a multiple linear regression test, the percentage of weight loss past 1 month, serum albumin, dyspepsia, dysphagia, lymphocytes, and gender (male) were the significant factors associated with malnutrition. Conclusion: UGIC patients are especially susceptible to malnutrition which might cause a decrease in therapy sensitivity, quality of life, and survival rate. Currently, proposed factors associated with malnutrition can assist in identifying UGIC-related malnutrition. Early nutrition screening and assessment followed with timely nutrition intervention is important to identify malnutrition and optimize nutrition status before treatment.