We measured the thermoelectric power of the organic conductor TTF[Ni(dmit)2]2 at the ambientpressure. The absolute thermopower at the ambient temperature is -46gmV/K. Its absolute value decreases with temperature, becomes positive at ca. 70K and downturns toward zero below ca. 35K. Our result shows that both TTF and Ni(dmit)2 chains contribute to the thermopower and their relative importance varies with temperature. Our results agree with other experimental investigations and could be understood in comparison with the calculated band structure.