OBJECTIVE To determine the dissociation constant of loratadine which is an insoluble alkalescent drug. METHODS Different acetone water mixtures were used instead of water to titrate.The pK-b was calculated by nonlogarithmic titration curves (Benet method). RESULTS The pK-b of loratadine was 8.581 9. CONCLUSION The method can be used for the determination of dissociation constants of insoluble alkalescent drugs