Postharvest storage conditions significantly impact the polyphenolic composition and antioxidant stability of pears (Pyrus spp.), which are crucial for fruit quality, shelf life, and nutritional value. Polyphenols, including flavonoids and phenolic acids, contribute to the antioxidant potential of pears, but their stability varies under different storage conditions. This study investigated the effects of cold storage (4°C, 85% RH), controlled atmosphere (CA) storage (2% O₂ + 3% CO₂, 2°C), and ambient storage (25°C, 60% RH) on the polyphenolic profile and antioxidant activity of pear fruit over 0, 15, 30, and 60 days of storage. Polyphenols play a vital role in delaying senescence and enhancing fruit defense against oxidative stress. Previous studies indicate that low-temperature storage reduces enzymatic oxidation, while CA storage minimizes metabolic degradation, preserving polyphenol levels. However, ambient storage accelerates oxidative reactions, leading to significant degradation. Although such storage effects have been well-documented in apples and berries, limited research has explored these mechanisms in pears. In this study, polyphenols were quantified using high-performance liquid chromatography (HPLC), while antioxidant activity was evaluated through DPPH and ABTS assays. The enzymatic activity of polyphenol oxidase (PPO) and peroxidase (POD) was also measured to assess oxidative degradation. The results showed that CA storage best preserved polyphenol content, followed by cold storage, whereas ambient storage led to significant degradation (p < 0.05). Chlorogenic acid and quercetin derivatives exhibited the most substantial losses under ambient conditions. Antioxidant assays confirmed that pears stored in CA conditions maintained higher antioxidant activity, while enzymatic analysis indicated significantly lower PPO and POD activities under CA and cold storage, reducing oxidative damage. These findings suggest that CA storage effectively delays polyphenol degradation by reducing oxidative stress and enzymatic activity, thereby maintaining the antioxidant properties of pears. This supports the growing use of CA storage for prolonging fruit shelf life while preserving bioactive compounds. Future research should explore metabolomic and transcriptomic approaches to further elucidate the molecular regulation of polyphenol metabolism in pears during postharvest storage.