The following optical crystallographic data for five esters of p-hydroxybenzoic acid have been determined: The principal indices of refraction, α, β, and γ; the birefringence, B; the optic sign; the type and extent of dispersion; elongation; habit; crystal system; extinction; and the αβγ3. The size of the optical axial angle, 2V, has been calculated from the indices of refraction, α, β and γ. The optical orientation has been noted when constant. The optical crystallographic constants allow rapid identification of the esters of p-hydroxybenzoic acid. The methyl ester can be readily recognized by the extremely strong anomalous dispersion and the small optic axial angle. The benzyl ester can be distinguished from the rest of the group by the positive optical character. The other three esters can also be rapidly identified by a combination of constants.