This study investigates the effects of ultrasound, in combination with chemical pretreatments, on the quality attributes (total phenolic and carotenoid content, antioxidant activity (2,2-Diphenyl-1-picrylhydrazyl assay (DPPH)), ferric-reducing ability (FRAP), CIE L* a* b* color, non-enzymatic browning, rehydration ratio, textural and morphological properties) of red pepper subjected to drying (hot air drying or freeze drying). The fractional factorial design was used to assess the impact of factors. The global Derringer desirability function was used to determine the optimal conditions for the best quality attributes of dried pepper. The drying method influenced total phenolic content, a* (redness), and initial rehydration ratio; pretreatment time significantly affected FRAP antiradical activity, a*, chroma and non-browning index, while pH-value had a significant effect on the texture of dried pepper. Non-enzymatic browning was reduced to 72.6%, while the DPPH antioxidant capacity of freeze-dried peppers was enhanced from 4.2% to 71.9%. Ultrasonic pretreatment led to changes in the pepper morphology, while potassium metabisulfite (KMS) was a more effective additive than citric acid.