Intra-regional fish trade has potential in addressing the region’s food and nutrition insecurity, as well as poverty reduction, by enabling movement of fish from countries of surplus to those with deficit. However, informal fish trade, just like all informal economic activities, has been overlooked and neglected in many national and regional policies, leading to obscurity of such an important part of the fisheries sector. This study examined the situation in the cross-border informal fish trade to deepen our understanding about the traders, the factors influencing the traders to use informal trade channels, the structure of the products traded and the challenges traders face, as well as propose policy direction to enhance the cross-border fish trade in the Southern Africa region. The study revealed that female traders dominated informal fish trade. In both Malawi and Zambia, an estimated 45,285.52 metric tonnes of fish valued at 82.14 million dollars and 102,263.9 metric tonnes of fish valued at 3.3 million dollars were informally traded. The key species involved in informal cross-border trade in Malawi and Zambia were the small pelagics, usipa (Engraulicypris sardella) from Lake Malawi and dagaa (Rastrineobola argentea) from Lake Tanganyika, respectively. It emerged from focus group discussions with informal fish traders and key informants’ interviews with border post fish inspection and revenue collection officials that traders are put off by the cross-border regulations. Therefore, it is important for countries in the Southern African Development Community (SADC) region to regularize and formalize cross-border trade, particularly in small pelagic fish species, since this species plays a great role in the livelihoods, food and nutrition security of many people in the region, especially the rural and urban poor. It is also important for governments to support processors and traders to improve the quality of fish being traded, and decentralize issuing of the import/export certificates and other cross-border support documents. Lastly, there is a need to establish informal fish trade monitoring systems to adequately quantify the volumes traded.