A reliable method is developed for preparing tantalum pentoxide film targets in natural water and biological fluids (urine, blood plasma and serum) by the anodization of tantalum metal using a current limiting constant voltage method. Tantalum pentoxide film targets are successfully prepared at a current density of 10 mA cm(-2) at an anodic voltage ranging from 20 V to 100 V without any oxide breakdown. The results show that for the same applied voltage, more ionic concentration in biological solutions leads to a higher rate of oxide growth than in water and a darker interference color. The analysis shows that anodic oxidation is more likely to breakdown in a biological environment than in pure water for the same oxidation time and applied voltage. The oxide film capacitance is found to be only slightly dependent on pH and anodic voltage with higher capacitive films in biological solutions than for water.