Alkylation of phenol with t-butanol in the vapour phase on SAPO-11 catalyst has been studied. The main products are 4-t-butylphenol, 2-t-butylphenol and 2,4-di-t-butylphenol, the last of these is the product of further alkylation of the 2-t-butylphenol. 2-t-butylphenol easily isomerises to 4-t-butylphenol whereas the reverse reaction is not significant. Separate Studies have shown that both butylphenols undergo easy dealkylation. The results of acid site poisoning by adsorption of bases as well as by sililation suggest that the reaction takes place essentially inside the zeolite pores.