A method and apparatus for transmitting frames having a long training field (LTF) for a second type of station (STA) in a wireless communication system are provided. For this, STA prepares a frame having a first part for a first type of STA and a second part for the second type of STA; wherein the second part includes multiple LTFs, when the frame is used for MU (Multiple User) transmission scheme or OFDMA (Orthogonal Frequency Divisional Multiple Access) scheme. In case a first LTF having a first number of symbols length and a second LTF having a second number of symbols length, which is greater than the first number of symbols length, are used for the multiple LTFs, the first LTF is extended such that the first LTF and the second LTF have a same number of symbols length. The STA transmits the prepared frame to one or more STAs.