Alkylation of biphenyl with t-butanol under liquid phase conditions has been studied over HY and H beta zeolites with different silicon to aluminum molar ratios as catalysts. HY zeolites have been shown to be more active than H beta zeolites. A maximum of 58% for the biphenyl conversion has been obtained over HY (15) zeolite at 160 degrees C. The initial catalytic activity of studied zeolites for t-butylation of biphenyl at 160 degrees C can be set in the next order: HY (15)>HY (30)>H beta (12.5)congruent to H beta (25). Both types of zeolites showed a significant selectivity of the monoalkylation step versus di- and polyalkylation with a very high selectivity leading to the 4-t-butylbiphenyl derivative (4-TBB) (near 95% for HY and 87% for H beta). Moreover, a high initial selectivity in 4,4'-di(t-butyl)biphenyl (4,4'-DTBB) was obtained (near 82% for HY and 90% for H beta at 160 degrees C). Such a selectivity remained constant with time over Ilk: while it dramatically decreased over H beta. Higher temperatures and higher catalyst concentration led to an increase of secondary reactions, which have been evidenced as isomerization of 4-TBB to 3-TBB, 4,4'-DTBB to 3,4'- and 3,3'-DTBB, oligomerization of isobutylene, alkylation of biphenyl with oligomers to higher alkyl- and polyalkylbiphenyls together with disproportionation and transalkylation of alkylbiphenyls.