Thermoelectric properties of three-dimensional covalently connected carbon networks are investigated by using first-principles calculation, Boltzmann transport theory, and nonequilibrium molecular dynamics simulations.It is found that the electronic transport of such networks exhibit "ballistic transport" behavior, similar to single carbon nanotubes, owing to the high power factor and largely reduced thermal conductivity The ZT value of carbon network (9,0) at intermediate temperature can be increased to 0.78 by n-type doping with a carrier concentration of 3.9 × 1019/cm3.Therefore carbon networks are expected to be potential candidates for eco-friendly thermoelectric materials.