In this paper we report the influence of the absolute surface area (ASA) and aspect ratio (L/D) of hydrothermally grown ZnO nanorods (NRs) on the NO2 and H-2 gases relative responses (RRs) in the 20 ppb - 1 ppm and 50 ppm-1000 ppm concentrations range. We used films of NRs characterized by different geometrical features, such as diameter, length, L/D and ASA, obtained using different growth times, but all showing a well-defined hexagonal shape and an alignment perpendicular to the substrate. Values of L/D up to 129 and NRs lengths up to 14 pm have been obtained; one of the highest reported for quasi-one-dimensional ZnO nanostructures obtained through solution-based one-pot syntheses. Electrical tests at 150 degrees C (NO2) and 200 degrees C (H-2) carried out using films of NRs presenting different L/D evidenced a direct relationship between the increase of the ASA and LID and gas RRs.The influence of geometrical and chemical characteristics, such as diameter, size and surface-defects concentration is also discussed in light of the existing literature. Cross sensitivity, investigated measuring the H-2 (target) response in the presence of NO2 (interfering) gases as well as dynamic and cumulative NO2 gas reproducibility test are also presented. Beside the considerable interference played by NO2 to the H-2 response, our long NRs demonstrate an excellent reproducibility of the electrical signal and fast recovery of the base line, evidencing the absence of irreversible chemisorption or sample-surface "history-related" phenomena. (C) 2016 Elsevier B.V. All rights reserved.