Protected area (PA) downsizing has been documented worldwide, but associated challenges on biodiversity and large mammal conservation in Chirisa Safari Area (CSA) are poorly understood. This study assesses the challenges associated with CSA downsizing on large mammals and biodiversity conservation. Field observations and face-to-face interviews were done with park management of CSA and SWRI from the 28th May 2021 to 10th June 2021. Analysis of station records on illegal activities, human-wildlife conflict (HWC) reports and land cover changes from 2010 to 2020 was also done. Poaching, encroachment by local people and veld fires, habitat fragmentation and HWC were sighted as major threats to large mammal biodiversity conservation in CSA. Analysed land cover and land use changes show evidence of the expansion of cultivation land and human settlements into areas that previously served as wildlife habitats. These changes have implications on large mammal and biodiversity conservation in CSA related to species migration, population decline, habitat loss and conflicts. We recommend that further research be undertaken in other areas affected by downsizing in Zimbabwe to aid knowledge in explaining its effect on large mammals and biodiversity conservation in adjacent PAs.