Shape memory effect (SME) of Co-Ni alloys was studied in terms of Ni content, epsilon martensite amount, and thermal cycling. The SME of solution treated Co-X%Ni alloys increased with the decrease in Ni content and with the increase in thermal F martensite content, while the influence of strain-induced epsilon martensite on SME is insignificant. Thermal cycling between 453degreesC and room temperature improved the SME of solution treated Co-Ni alloys by increasing thermal epsilon amount.