The large group delay of high order FIR filters is unacceptable in some applications. So, recently, methods to reduce the group delay of FIR filters have been studied intensively. To reduce the ringing in the time domain and to maximize the stopband attenuation, it is useful to design FIR filters with maximally flat characteristics in the passband and transmission zeros in the stop band. We present a mathematically closed form transfer function of low delay lowpass FIR filters with maximally flat amplitude in the passband and the transmission zeros in the stopband. Therefore, the designed filters are very simple. Moreover, we present also a design method of low delay lowpass FIR filters with maximally flat amplitude in the passband and equiripple in the stopband by using an iterative method of a closed form transfer function and the Remez algorithm.