This paper presents a generation method of orthogonal spreading codes with different spreading factors (SFs), which are called orthogonal multi-SF spreading codes in this paper, for DS-CDMA mobile radio. The generated orthogonal multi-SF spreading codes have a tree structure and the codes are applied to the forward link such that all users, who transmit data at different rates, are orthogonalized. A group spreading modulator that simplifies the base station transmitter structure is also described. The transmission performance of the orthogonal multi-SF forward link under multi-user and frequency selective Rayleigh fading environments is evaluated by computer simulation to show that its performance is identical to that achieved by using multiple orthogonal spreading codes in parallel (orthogonal multicode forward link). Unlike the orthogonal multicode forward link, only a single Rake combiner is required at a mobile receiver which significantly simplifies the mobile receiver structure.