Peas (Pisum sativum L.) are among the most widely cultivated legumes, known for their adaptability to dry and warm environments and their high nutritional value. This research aimed to investigate the biochemical diversity of proteins, polyphenols, flavonoids, tannins, and antioxidant activity in a local population of peas from the Mareth oasis in Tunisia under different preservation methods: fresh, frozen, canned, and dried. The hypothesis was that preservation methods significantly impact the nutritional quality of peas, with fresh peas retaining the highest levels of essential nutrients. The results showed that fresh peas had superior nutritional quality, demonstrating the highest concentrations of protein (39 mg/g MF), polyphenols (0.17 mg GAE/g MF), flavonoids (0.086 mg QE/mg MF), and antioxidants (52%). In contrast, dried peas exhibited the lowest nutrient levels, particularly in protein and antioxidant activity. The study highlighted that freezing is an effective method for preserving the nutritional integrity of peas compared to canning and drying, which significantly reduce essential nutrient levels. Understanding the effects of various preservation techniques is crucial for maintaining the nutritional quality of peas. These findings have significant implications for consumers and the food industry, advocating for practices that prioritize the retention of nutrients in preserved peas. This research contributes to the ongoing discourse on food preservation methods and their impact on nutritional quality, providing insights that support better choices in food processing and consumption.