Acylation of biphenyl with acetic anhydride and carboxylic acids over zeolite catalysts is investigated. Acylation of biphenyl with acetic anhydride over zeolite HY and zeolite beta at 83 degreesC gives 4-acetylbiphenyl as the main product. The selectivity to 4-acetylbiphenyl is always higher than 98% and the highest yields are obtained over zeolite beta. An increase of the Si/Al ratio in zeolite beta leads to slightly higher rates of 4-acetylbiphenyl formation, however, the final yields are always within the range 8-10%. Catalyst deactivation occurs and is mainly due to product inhibition, i.e. 4-acetylbiphenyl strongly competes for the adsorption sites on the zeolite. Acylation of 4-acetylbiphenyl yielded less than 38 diacylated products, with a 4,4 ' -diacetylbiphenyl selectivity below 12%. Solventless acylation of biphenyl with hexanoic acid at 150 degreesC produces 4-hexanoylbiphenyl (selectivity > 98%) at a yield of 8-14% and the best results are obtained over zeolite HY. An increase in temperature enhances the yield of 4-hexanoylbiphenyl (53% at 200 degreesC) but decreases slightly the selectivity (similar to 92%). Acylation with a bulky acid (trimethyiacetic acid) in an attempt to obtain shape selective e acylation led to the formation of 4-t-butylbiphenyl as main product (yield similar to9%) instead of the acylated product.