Display omitted •The thermoelectric properties of metal-organic complexes are reviewed.•Empirical guidelines for thermoelectric research on metal-organic complexes are discussed.•Advantages and challenges of metal-organic complexes for thermoelectric application are presented. Recent research progress has drawn the attention to thermoelectric (TE) property of Poly(M-ett) (M=metal, ett=ethylenetetrathiolate), which provides the best performance of n-type organic thermoelectric (OTE) materials. Metal-organic complexes have been extensively studied for their applications in magnetism, catalysis, molecular storage, and luminescence etc. Now their potential for thermoelectric conversion technology is being explored. The research on thermoelectric effect of metal-organic complexes has a history of over 50 years, efforts were mainly focused on small molecular complexes in early studies, such as metal phthalocyanine complexes. Related research on Poly(M-ett) injects fresh vitality to the field of OTE materials. In this article, TE properties of metal-organic complexes are reviewed, including small molecular complexes and coordination polymers (CPs), empirical guidelines for OTE research on metal-organic complexes are discussed.