The conservation management literature has recently documented the increasing use of co-management approach to effectively conserve natural resources. Although most research qualify the co-management as highly effective, some authors also reported a number of uncertainties associated with the use of this conservation approach. Using the Mono Transboundary Biosphere Reserve (MTBR) as a case study, this work assessed the effectiveness of the co-management towards mangroves conservation in West Africa. Data were collected in two protected sites of the reserve (one in Togo and the other in Benin). Exploratory sequential mixed method via in-depth interviews (n=17), focus group discussions (n=14), household survey (n=274) and expert-based survey (n=10) were carried out, and subjected to the InVEST-based Habitat Risk Assessment (HRA) model, chi-square test and simple probability of likelihood. Results indicated that under the current co-management regimes, the anthropogenic stressors recorded in the reserve put the entire surface area of mangroves in Benin (100%) under low risk. Contrarily, 42% of the mangrove cover are under low risk and 58% under medium risk in Togo. Local perception also portrayed a large reduction of mangrove degradation in the study sites following the adoption of the co-management approach in the two countries. This study suggests that the implementation of the co-management approach has lowered anthropogenic stressors to mangroves in the reserve. However, there are some peculiar challenges (e.g., financial support provision, regular community engagement), which need to be thoroughly researched and addressed for a more effective conservation of mangroves in the MTBR.