Hydrodynamic characteristics of the flow induced by a four-bladed disk-style turbine in a stirred tank bioreactor were determined. A bioreactor with a vessel diameter ( T = 0.22 m), a fiat bottom and 4 baffles positioned away from the walls was used for the experiments. The impeller was located at the mid-height of the water level which was equal to tank diameter. Measurements of three-dimensional velocity components were made in a 45° plane between baffles. Dimensionless groups such as discharge flow number, circulation flow number, pumping index and hydraulic efficiency were calculated. The influence of increasing the blade area and blade number on the above-mentioned dimensionless groups was studied. Increasing the blade area has a stronger influence on the pumping index and the discharge flow number than the influence of increasing the blade number, and a lesser influence on the circulation flow number. However, for variation in both blade area and number, the influence on the hydraulic efficiency is similar. The correlation equations, to estimate the discharge flow number and mixing time in vessels with baffles close to the tank wall could be recommended for systems with 4 baffles positioned away from the wall as an error of less than 5% has been found.