ABSTRACT Background: The bariatric surgery may cause some nutritional deficiencies. Aim: To compare the serum levels of biochemical markers, in iimmediate post-surgical patients who were submitted to bariatric surgery. Methods: Non-concurrent prospective cross-sectional study. The analysis investigated data in medical charts of pre-surgical and immediate post-surgical patients who were submitted to bariatric surgery, focusing total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, C reactive protein, vitamin B12 levels, folic acid, homocysteine values, iron and serum calcium at the referred period. Results: Twenty-nine patients of both genders were evaluated. It was observed weight loss from 108.53 kg to 78.69 kg after the procedure. The variable LDL-c had a significant difference, decreasing approximately 30.3 mg/dl after the surgery. The vitamin B12 serum average levels went from 341.9 pg/ml to 667.2 pg/ml. The triglycerides values were in a range of 129.6 mg/dl-173.3 mg/dl, and 81.9 mg/dl-105.3 mg/dl at the pre- and postoperative respectively. CRP levels fall demonstrated reduction of inflammatory activity. The variable homocysteine was tested in a paired manner and it did not show a significant changing before or after, although it showed a strong correlation with LDL cholesterol. Conclusion: Eligible patients to bariatric surgery frequently present pre-nutritional deficiencies, having increased post-surgical risks when they don´t follow an appropriate nutritional follow-up.