A theoretical study of the cracking reaction of thiophene by small zeolitic cluster catalysts is reported. Cluster density functional theory calculations have been performed. It is shown that cracking of thiophene is catalyzed by Lewis basic oxygen atoms. Several active sites are proposed and tested. Moreover, it appears that the use of a partner molecule, strongly adsorbed to the acidic proton, allows for an important decrease of the cracking activation energy barrier. The effect of hydrogenation of thiophene prior to the cracking reaction has been checked. Interestingly, hydrogenation does not affect dramatically the activation energy barrier (-10 kJ/mol). However a large stabilization of the product of the reaction has been found (-40 kJ/mol).