It has been proposed that two isomers of the SO dimer (cis- and trans-OSSO) are candidates for the unknown UV absorber in Venus’ atmosphere because they have a good spectral match with the absorber, despite the low concentrations predicted by 1D photochemical models. Here OSSO chemistry (production from SO and loss by photolysis, thermal decomposition, and reaction with O and Cl) has been included in the photochemistry scheme of a 3D planetary climate model (PCM-Venus) along with sulphur injection due to meteoric ablation. 1D multiple scattering radiative transfer modelling is then used to predict the resulting top-of-the-atmosphere reflectance produced by OSSO. The modeled OSSO concentrations are shown to be ~3 orders of magnitude too low to explain the observed absorbance levels, and the predicted ratio of the OSSO isomers provides an unsatisfactory match to the spectral shape of the unknown absorber.