In this work an analysis of biodiesel fuel use in stationary engines was made through performance tests in dynamometer. In the tests, the characteristics of torque, power, specific consumption and smoke index were determined for two cylinders diesel engines. Initially, the engines were tested working with diesel, and then the tests were done with the engines working with diesel and biodiesel mixtures specified by B25, B50, B75 and B100. The biodiesel used on the tests was of soy. The results show that the use of biodiesel is feasible, but with loss of power and torque when compared to pure diesel. For pure biodiesel (B100) at 3,000 rpm the power decrease was 4.03% while for B50 the decrease was 0.94%. The results for torque showed a similar behavior with a decrease of 4.08% for B100 and 0.93% for B50 at 3,000 rpm. The specific consumption increased, as expected, 12.25% for B100 and 5.44% for B50. However, the use of pure biodiesel (B100) reduced the smoke index (Bosch Scale) from 4.5 to 3.0 at the higher speed and from 2.7 to 1.1 at the lower speed. The results indicate that the performance for B50 blend is almost the same of pure diesel while the emissions are lower. The thermal efficiencies were estimated and the operation with diesel showed lower values than the biodiesel blends, indicating that biofuels are a good alternative for fossil fuels.