To develop diverse anisotropic thin films, asymmetric bideposition technique is introduced to fabricate tilt columnar Ta2O5 films with biaxial optical property. The asymmetric bideposition is achieved using two different opposite deposition angles (a+,a-) and two different thicknesses of opposite deposited subdeposits. The two sets of Ta2O5 columnar thin films associated with deposited subdeposits (d+,d-)=(5.2,2.8) are prepared at the opposite deposition angles (a+,a-)=(70,-40), (75,-40), (80,-40) and at the opposite deposition angles (a+,a-)=(70,-50), (75,-50), (80,-50). Columnar thin films with various column angle and biaxial properties are measured their planar birefringence and three principal indexes. The larger column angle leads to higher principal indices. It is demonstrated that the asymmetric bideposition can enhance the birefringence of a tilted columnar thin film.ntut.edu.tw© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.