Studies demonstrate that obesity can increase tumor development. Botryosphaeran, a fungal (1→3)(1→6)-β-D-glucan, presents antimutagenic, antiproliferative and pro-apoptotic activities. This study evaluated the effects of botryosphaeran on tumor development and metabolic and hematological parameters in tumor-bearing obese and non-obese rats. Obesity was induced by a high-fat and high-sugar diet, while control rats received standard diet and water without sugar for 10 weeks. On 8th-week, Walker-256 tumor cells were inoculated in the rats, and treatment with botryosphaeran (12 mg/Kg b.w.) started. Groups:control tumor-CT, control tumor botryosphaeran-CTB, obese tumor-OT and obese tumor botryosphaeran-OTB. On 10th-week, tumor development, cachexia, metabolic and hematological parameters were analyzed. Tumor development and cachexia were significantly higher in the OT group compared to the CT group, and botryosphaeran attenuated these parameters. OT rats presented accumulation of adipose tissue, reduced muscle mass, glucose intolerance, insulin resistance, hyperglycemia, anemia, leukocytosis, and thrombocytopenia. Botryosphaeran corrected insulin resistance and hyperglycemia, modulated cholesterol levels, and increased leukocyte and lymphocytes in obese rats, which can be attributable to an inflammatory response against the Walker-256 tumor, contributing to a lower tumor development. Our data demonstrated that botryosphaeran was effective in attenuating tumor growth and in improving the metabolic and hematological profiles of the tumor-bearing rats, demonstrating its potential role in the cancer’s management.