Lee et al. proposed two methods to speed up the computation of scalar multiplication of elliptic curve defined over GF (2(superscript mn)) with a medium size of m in the range 10≤m≤20. In these methods, Frobenius map is utilized to expand the integer k and each coefficient of the expansion is represented as a binary string. In this pa- per, with the application of joint sparse form (JSF) to the coefficients, some variations of Lee et al.'s methods are proposed to achieve a better performance at a lower storage requirement.