A new red butterhead lettuce (Lactuca sativa L.) with transverse broad elliptic, red leaves, ‘Sun Red Butter’, with late bolting and high yield, was developed from a cross between ‘Jajusangchu’ (red leaf color and half crisp) and ‘Dukseomjeokchukmyeon’ (high yield). The crossing and selection for advanced lines was previously carried out using the pedigree method during the period 2001–2009. The advanced lines were evaluated for yield and adaptability at several locations in Korea (Gangwon-do, Gyeonggi-do, Chungcheongbuk-do, Jeollabuk-do, Gyeongsangnam-do, and Jeju-do) in 2011. The type of matured stage is early and medium butterhead lettuce. The shelf life of ‘Sun Red Butter’ was four weeks longer than that of ‘Germania’ at 4°C. The anthocyanin content of ‘Sun Red Butter’ was lower than that of ‘Germania’ at 11.2 mg/100 g. The BSL (latucin+8-deoxylactucin+lactucopicrin) content of ‘Sun Red Butter’ was higher than that of ‘Germania’ at 32.8 µg/g, DW. The marketable yield of ‘Sun Red Butter’ was higher than that of ‘Germania’ by 67% (at 621.4 g per plant), and ‘Sun Red Butter’ showed a particularly improved yield under high-temperature cultivation in the field. Furthermore, ‘Sun Red Butter’ had better taste characteristics and was crisper and sweeter than ‘Germania’. Therefore, we recommend that the new cultivar ‘Sun Red Butter’ would be suitable for cultivation in spring and fall. Furthermore, this new cultivar could be harvested in a single harvest, as in a head lettuce, and could therefore be managed more efficiently and economically by farmers.