Cost-efficient fabrication of cathode catalyst layer having low Pt-loading and high oxygen reduction reaction (ORR) performance is of prime importance towards commercialization of low temperature fuel cells. Here, an attempt has been made to fabricate hierarchically structured and cathode catalyst layer consisting of Pt-nanoparticle clusters supported on defective carbon nanotube (CNT) coated carbon fiber (CNTCF). CNTs are grown on carbon fiber (CF) by chemical vapor deposition (CVD), while electrodeposition is employed to deposit Pt-nanoparticle clusters on the CNTCF. Effect of Pt-loading on oxygen reduction reaction (ORR) performance of the Ptcoated CNTCF (Pt-CNTCF) electrocatalysts is studied by varying the electrodeposition time (ted) between 5 and 30 min, which results a variation of Pt weight fraction in Pt-CNTCF from almost zero to ~0.3. Linear sweep voltammetry using the Pt-CNTCF modified glassy carbon (GC) rotating disc electrode (RDE) is employed to study the ORR performance of the samples. The CNTCF support, owing to the defective structure of CNT, itself exhibits significant ORR activity with an electron transfer number (n) of ~2.6, which leads to a synergistic enhancement of the overall electrocatalytic performance of Pt-CNTCF. For lower Pt-loading on GC (~5 μg cm -2 ), the contribution of CNTCF support dominates, while the Pt-nanoclusters govern the ORR 2 performance at higher Pt-loading ((>10 μg cm -2 ), with n>3.5. Hence, a very low Pt-loading (~5 μg cm -2 ) may not be suitable for polymer electrolyte membrane fuel cells as production of substantial amounts of H2O2 on the catalyst supports may accelerate the membrane degradation.