The chlorine concentration in trichloroisocyanuric acid (TCI) solutions depended on the solvent used to apply the chlorination agent on the rubber surface and on the time after preparation of the solutions. In this study, methyl ethyl ketone (MEK) and ethyl acetate (EA) have been used as solvents for 2 wt% TCI in the treatment of a difficult-to-bond synthetic vulcanized styrene-butadiene rubber (R2 rubber). Chlorination produced improved wettability of the R2 rubber and also the removal of paraffin wax from the surface. Furthermore, several C-Cl and C=O moieties are produced, and some microroughness was created. The concentration of chlorine in the 2 wt% TCI/MEK solution decreased by increasing the time after preparation, and the effects due to chlorination became less marked by increasing the time. However, the concentration of chlorine in the 2 wt% TCI/EA solution was higher and was not noticeably decreased by increasing the time after preparation, and noticeable surface modifications were produced on the R2 rubber treated with the chlorinating solution 6 weeks after preparation. The improved surface modifications of R2 rubber allowed an increase in adhesion to polyurethane adhesive, and the failure was cohesive in the chlorinated layer. A relationship between the chlorine concentration in the TO solution and the peel strength value in treated R2 rubber/polyurethane adhesive joint was obtained.