According to Maxwell equations and boundary conditions of electromagnetic field, the general dispersion equations are reduced for the guided modes in rectangular dielectric waveguides. The field distributions of the guided modes are numerically simulated for the waveguides with ordinary dielectric materials and the rectangular waveguides with left-handed materials (LHMs), respectively. The simulation results show that field distribution of the Ex22 mode is restricted mainly in the central part of waveguide with LHMs compared with that of Ex00 mode of the waveguide with dielectric materials. Based on Marcatili's method, the dispersion equation of surface guided modes in rectangular waveguides with LHMs is deduced, and the field distribution of lower-order modes is numerically simulated. The results show that energy of field mode is located mainly in the four angles and edges of waveguide with LHMs.