TiO2 nanopowders with different morphologies and initial anatase contents (f(A)) were synthesized by gliding arc plasma. X-ray diffraction (XRD), transmission electron microscope (TEM) and physisorption instruments were employed to investigate the effects of calcination temperature on phase composition, crystal size, morphology and specific surface area (S-BET) of the TiO2 nanopowders. Photocatalytic oxidation of methylene blue was utilized to evaluate the activities of calcined TiO2 nanopowders. The results indicate that the anatase-rutile transformation temperature of as-synthesized TiO2 nanopowders is around 650 degrees C, and the anatase-rutile transformation rate depends on the calcination temperature, morphology and the initial fA. With the increase of calcination temperature, the anatase crystal size slightly increases and S-BET slightly decreases for spherical particles, while for non-spherical particles, the anatase crystal size increases and S-BET decreases rapidly. With the increase of f(A), the variation of photocatalytic apparent rate constant (k) of TiO2 nanopowder presents three profiles: when f(A) is below 70%, k slowly increases; when f(A) ranges from 70% to 85%, k rapidly increases; when f(A) is beyond 85%, k rapidly decreases.