Calculation of parameters of quantum fluctuations of pulses generated in fiber lasers with mode synchronization or in nonlinear fiber ring resonators is presented. Quantum fluctuations are associated with fluctuations in the amplitudes and phases of longitudinal modes. Using standard mode oscillator quantization, expressions are recorded for sources of amplitude and phase fluctuations for each longitudinal mode. In this case, phase fluctuations are calculated by amplitude using Heisenberg relations. It was assumed that the fluctuations in the amplitudes of the modes obey the Poisson distribution, and the sources of fluctuations in the time-domain are obtained using the inverse discrete Fourier transform. For a pulse of sech(t)², fluctuations in quantum number, pulse maximum time, chirp and phase are calculated. Keywords: Mode locking, quantum fluctuations, spectrum of longitudinal modes, sech^2-pulse, pulse parameters fluctuations.