Edible plant parts are a rich source of bioactive molecules. By-products from vegetal sources offer the chance to reclaim them by expropriating the bioactive molecules. Phytochemicals in vegetables protect plants, have health benefits, and reduce disease risk. This chapter reported on cauliflower (Brassica oleracea) by-products used in the human diet and intends to provide further insight into a nutritional evaluation. Brassica vegetables are a valuable source of phytochemicals, including glucosinolates, phenolic compounds, and carotenoids. Organosulfur compounds are a subgroup of phytochemicals found in cauliflower. In addition, glucoraphanin is a glucosinolate reported in B. oleracea var. botrytis and is considered one of the main cauliflower phytochemicals. Bioactivity studies have been conducted using plain phytochemicals of cauliflower and showed potential biological activities. The crude extracts from the cauliflower by-product were used for a radical scavenging assay and exhibited DPPḤ radical scavenging potential, lipid peroxidation inhibition, and hydroxyl radical scavenging activity. Future outlooks for researchers on nutrition, processing, packaging, food quality, and industries dealing with agricultural products include expanding research on cauliflower by-products as a hidden source of phytochemicals.