Damage to intestinal mucosa may impair nutritional status and increase the demand for nutrients involved in intestinal cell proliferation (retinol and folate). It is still unclear if cytotoxic therapy affects serum concentrations of these nutrients in patients with cancer and if this would be associated with disturbances of intestinal mucosa. Intestinal permeability, serum folate, and retinol and nutritional status of 22 patients with hematologic malignancies and 17 healthy volunteers [control group (CG)] were assessed before (T0) and after cytotoxic therapy (T1). Ingestion of lactulose and mannitol was used to assess intestinal permeability. Anthropometric, body composition, phase angle (PA), and biochemical analysis (albumin, retinol, and folate) were also performed. Lactulose/mannitol ratio (0.026 ± 0.014 vs. 0.052 ± 0.037) and lactulose excretion (0.27 ± 0.18% vs. 0.53 ± 0.6%) increased at T1. PA decreased (7.2 ± 1.9° vs. 6.2 ± 0.9°). Serum folate and albumin (20.7 ± 9.5 nmol/L, 37.7 ± 5.5 g/L) were lower than CG (39.2 ± 16.4 nmol/L, 42.9 ± 5.2 g/L) but did not change at T1 (17.5 ± 7.0 nmol/L, 35.9 ± 4.5 g/L). Serum retinol did not differ from CG and did not change at T1 (1.83 ± 0.30 μmol/L vs. 1.69 ± 0.3 μmol/L; CG: 1.86 ± 0.20 μmol/L). Abnormal intestinal permeability, low serum folate levels, and its possible relationship with intestinal alterations, and reduced PA, may be associated with poor nutritional status in cancer patients.