Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI-DBSA) / multi-walled carbon nanotube (MWCNT) nanocomposites (PANI-DBSA/MWCNT) based gas sensor is prepared and characterized for ammonia gas, prolonged exposure of which results in many potential health hazards such as rapid skin irritation, olfactory fatigue, cellular destruction and tissue necrosis. Highly conducting dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI-DBSA) / multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by in-situ polymerization process. FESEM, TEM, XRD, and UV-visible measurements confirmed the formations of PANI-DBSA/MWCNT nanocomposites. Experimentally it is observed that thin film of PANI-DBSA/3wt.%MWCNT nanocomposites synthesized by indirect doping route provides better ammonia gas sensing response (2.65 at 100 PPM) as compared to thin film of nanostructured PANI-DBSA (1.25 at 100 PPM). The cross-selectivity results revealed that the developed sensor is highly selective to ammonia gas as compared to other gases. © 2019 IEEE.