The optical transitions in InGaN/AlGaN single quantum wells (SQWs) grown by metal-organic chemical vapor deposition have been studied, The spectral lineshape and the recombination dynamics of the optical transitions have been systematically investigated at different conditions. It was found that the main photoluminescence (PL) emission line in these SQW was contributed predominantly by the localized exciton recombination. However, time-resolved PL results revealed the presence of a band-to-impurity transition which cannot be resolved spectroscopically from the localized exciton transition line due to the broad emission linewidth.