Present work is an investigation of the inter-relationship between nanostructures of conducting polyaniline (PANI) and photocatalytic efficiencies of its composites with anatase TiO2. Two composites with/without ultra-sonication (PANI-TiO2-S and PANI-TiO2) of the polymerization mixture and pristine PANI were prepared by in situ chemical oxidation method. IR and XRD characterizations revealed the core (TiO2) - shell (PANI) arrangement of the hybrid composites. PANI-TiO2-S had nanorods structures grown with TiO2 template and some irregularly shaped secondary grains; but PANI-TiO2 had only spherical submicron size particles. In visible light photodecomposition of methylene blue, PANI, TiO2, PANI-TiO2-S and PANI-TiO2 had the efficiencies of 58%, 71%, 77% and 65% respectively. The greatest efficiency of PANI-TiO2-S originated from the nanostructures of PANI and the combined effect of PANI and TiO2 components in hybrid. Besides this, the characteristics of composites remained invariable during photocatalytic run, which facilitated retain of efficiency during second/third run. (C) 2013 Elsevier Ltd. All rights reserved: