Zeolites p and mordenite were impregnated with 0.1 wt.% Pt and varying (0, 0. 1, 0.3 and 0.5 wt.%) amount of Ni and reduced at 475 degreesC. The line broadening XRD analysis indicates that the increasing Ni addition decreases the crystallinity of zeolites. The TEM analysis indicates that the average metal particle size increases with increasing Ni addition. The states of Ni and Pt were analysed by ESCA. The acidity measurements by both TPD of ammonia and pyridine adsorbed FT-IR spectroscopy show the occupation of some of the acid sites by the added Ni species. Hydroisomerisation of n-heptane was carried out in the temperature range 225-375degreesC and found that Ni addition up to 0.3 wt.% over 0. 1 wt.% Pt/H-beta and 0. 1 wt.% over 0. 1 wt.% Pt/H-MOR enhance the n-heptane conversion, isomerisation selectivity and sustainability of the catalysts. Also, the multibranched (MTB) isomers selectivity and protonated cyclopropane (PCP) intermediate mechanism are favoured over the above catalysts. Further Ni addition above the threshold value leads to fall in activity and isomerisation selectivity drastically. Zeolite-beta based Ni-Pt catalysts always show higher activity and selectivity than mordenite based catalysts. (C) 2003 Elsevier B.V. All rights reserved.