The invention provides a zeolite of the faujasite structure which has a unit cell size in the range of from 24.40 to 24.50 .ANG.; a bulk silica to alumina ratio (SAR) in the range of from 5 to 10; and an alkali metal content of less than 0.15 wt %. Such zeolites have been found to have a very useful naphtha selectivity in hydrocracking, particularly a selectivity to heavy naphtha. A preparation process for the zeolite, hydrocracking catalyst composition comprising the zeolite and its use in hydrocracking are also provided.