The photochemical decomposition of aqueous phenyl diazosulphonate solutions by KrF excimer laser pulses at 248 nm is investigated. The present study complements earlier investigations (Franzke et al. 1991, 1992) of the photochemistry of this class of compounds induced by irradiation at 308 nm (XeCl excimer laser), and in the 370–390 nm wavelength range (dye laser pulses). From the comparison, conclusions with regard to the wavelength dependent photolysis pathway are drawn. Phenyl diazosulphonates carrying methoxy‐ or ester‐type substituents at the aromatic ring are observed to decompose in a two‐step‐reaction in aqueous solution: Photolysis proceeds via the phenyl diazonium ion as an intermediate, to yield the corresponding phenol as a product. In contrast, the photolysis of 3‐vinyl‐phenyl diazosulphonate in aqueous solution at 248 nm results in a complex reaction involving via more than one intermediate. UV spectra recorded during photolysis show that products characterized by an absorption maximum at 272 nm are formed; these spectra are identical with those of final products from 308 nm photolysis, which are identified as 3‐hydroxyethyl‐phenols. – The photolysis pathway of 4‐hydroxy‐phenyl‐diazosulphonate is found to proceed via the diazoquinone, instead of a diazonium ion. As a consequence of the high energy of 248 nm photons, the mentioned substituted phenols are not the final products of the photochemical reaction. These molecules are further decomposed by absorbing 248 nm photons; the quantum efficiency of these secondary photochemical reactions is lower by one to two orders of magnitude, as compared to the primary photolysis of the parent compounds.