Vapour phase butylation of phenol was carried out over a sulfated zirconia solid superacid catalyst in the temperature range 448-473 K using t-butyl alcohol as the alkylating agent. A good substrate (phenol) conversion and excellent product (para-tertiary BP) selectivity was obtained. The catalytic activity remains nearly the same on repeated use of the catalyst. Further, the catalyst was not deactivated when the reaction was carried out for a longer duration, i.e.. even after several hours of reaction.