The present invention relates to an apparatus and method of acquiring initial synchronization of a terminal in a mobile communication system. According to an exemplary embodiment of the present invention, one or more auto-correlation values of a preamble constituting a signal that is received from a base station are calculated. Averages of the calculated auto-correlation values according to samples are calculated, and then a peak value is detected among the calculated values. Then, a cell search is performed on the basis of the detected peak value, and a peak value from the result of the cell search is regularized. Then, the regularized peak value is compared with a predetermined reference value such that it is checked whether synchronization of a signal that has been searched is accurate or not. According to an exemplary embodiment of the present invention, a value obtained by regularizing a result of a cell search is compared with a reference value, and it is checked again whether an accurate start point of a frame is detected or not on the basis of a result of the comparison. Accordingly, false alarm rates can be reduced.