Tanneries use chromium in tanning animal skin, providing strength and durability for leather. Organic load is already arising from the parties that are removed from the skin of the animal during the washing process. This organic material into water can be degraded by microorganisms, which during the process of consuming the oxygen dissolved in water. The advantages of using microorganismos in wastewater biotreatment process is high selectivity, low cost, resuse and have a possible influence of magnetic fields on their biological systems, so the use of magnetic field can be a new tool for research. This work has studied the biological degradation of waste chromium (80 mg/L) using a mixed culture of microorganisms, pH 6, to a stirred tank reactor with constant mechanical stirring (550 rpm) coupled to a tubular reactor where the effluent was pumped in the magnetic field. The same system of treatment was performed without the application of the field. In the first use of the microorganisms (Test 1) the removal of organic matter after 28 hours was 92,36% and 93,50%. In the first reuse of the cells (Test 2) was 91,81% and 93,09%, with and without the application of the field, respectively. The second reuse (Test 3) there was a final removal of the organic load of 73,39%, with no field and 91,90% in the treated effluent field, thus showing that the field influence the behavior of the mixed culture.