The H-ZSM-5 zeolite catalysts were synthesized by varying the synthesis time and mode of stirring. The catalysts were characterized using X-ray powder diffraction, scanning electron microscope, X-ray fluorescency, nitrogen adsorption and FTIR of adsorbed pyridine. It was found that the synthesis time and mode of stirring influenced the morphology, phase purity, surface area, acidic and catalytic properties of H-ZSM-5. The XRD patterns of Na-ZSM-5 zeolite synthesized in 3 and 6h exhibited the presence of amorphous phase. The crystal size of ZSM-5 increased with increase in synthesis time. The FTIR spectra of adsorbed pyridine on H-ZSM-5 catalysts synthesized in 72, 24 and 12 h showed the presence of Brønsted and Lewis acid sites. The H-ZSM-5 catalyst synthesized in 72 h exhibited highest number of Brønsted acid sites. The reaction of n-butane to iso-butane was used as a test reaction to investigate the catalytic property of the synthesized H-ZSM-5 catalysts. The effect of time on stream, temperature and weight hour space velocity (WHSV) on the conversion of n-butane and yield of iso-butane over the H-ZSM-5 catalysts were studied. The H-ZSM-5 catalyst synthesized in 72 h in the static mode showed the highest conversion of n-butane and yield of iso-butane. © 2002 Elsevier Science B.V. All rights reserved.