Red-fleshed apples are preferred because of their high content of phenolics and antioxidants. In this study, the phenolic characteristics, antioxidant properties, and antihuman cancer cell properties of the four hybrids of Malus sieversii f. niedzwetzkyana (Ledeb.) M. Roem were analyzed. In addition, the antioxidant and anti-proliferation properties of these apples were measured. Compared to "Fuji" apples, the red-fleshed apples were rich in phenolic and flavonoid chemicals, ranging from 1.5- to 2.6-fold and 1.4- to 2.4-fold, respectively. In all antioxidant methods (DPPH radical-scavenging capacity, ABTS radical scavenging activity, ferric reducing antioxidant power, and cell antioxidant capacity), "A38" obtained the highest antioxidant value, whereas "Fuji" got the lowest antioxidant value. The IC₅₀ values ranged from 33.44 ("A38") to 73.36 mg/mL ("Fuji") for MCF-7 and 20.94 ("A38") to 39.39 mg/mL ("Fuji") for MAD-MB-231. The red-fleshed "A38" and "Meihong" exhibited higher antioxidant and antiproliferative activities in vitro because of the higher levels of phenolics, and the higher potential for development and utilization value. PRACTICAL APPLICATION: The phenolic compounds, antioxidant activity, and antiproliferative activity in vitro of four red-fleshed apple cultivars and one white-fleshed apple cultivar were compared in this study. This information should assist to give a reasonable evaluation for scientists to breed new cultivars with high phenolics and to exploit the natural polyphenol.