Nanotubular oxide layer formation on biomedical grade alpha + beta type Ti-13Nb-13Zr alloy was investigated using anodization technique as a function of applied dc potential (10-40 V) and anodizing time (30-180 min) in 1 M H3PO4 + 0.5 wt% NaF at room temperature. The as-formed and crystallized nanotubes were characterized using SEM, XRD, and TEM. There was a bimodal size distribution of nanotubes with diameters at the range of 25-110 nm. Nanotubes nucleated on beta matrix exhibited uniform surface appearance with circular morphology, whereas those nucleated on alpha phase yielded parabolic shape. TEM/EDS analysis detected the three component elements of the alloy in the nanotube. Heat treatment significantly altered the distinct interface between the nanotubes and the barrier oxide layer.