The aim was to investigate the serum levels of leptin, TNF-alpha, IL-1 beta, IL-6, insulin, and growth hormone in patients with upper gastrointestinal cancer and cachexia. A total of 39 patients with various advanced stage (stage IV) gastrointestinal malignancies were enrolled. These cancer patients were divided into two groups according to the presence or absence of cachexia. Fifteen healthy adults were recruited as the control group. Body mass index (BMI; kg/m2) was calculated. Serum leptin, tumour necrosis factor (TNF)-α interleukin (IL)-1 beta, interleukin (IL)-6, growth hormone, insulin, glucose, triglyceride, total protein, albumin, erythrocyte sedimentation rate, and CRP were measured. In both cancer groups (cachectic and non-cachectic) body mass index and serum leptin levels were lower than controls (p < 0.001). Serum IL-1 beta, IL-6, and growth hormone levels were higher in both cachectic and non-cachectic groups than those of controls (p < 0.05). Serum TNF-α level in non-cachectic group was also significantly higher than in control group (p < 0.01). There is no significant difference between three groups in terms of insulin resistance as assessed by HOMA index. Our results showed that some proinflammatory cytokine levels were increased and leptin level was decreased due to upper gastrointestinal cancers. Increased cytokine levels may lead to decreased food intake and caused a weight loss.