Summary There have been calls for the expansion of protected areas (PAs) to tackle the ongoing biodiversity loss, yet it is unclear where future PAs might help to protect biodiversity in degraded landscapes under the conservation planning principles of complementarity, connectivity and cost-effectiveness. Our conservation goal is to increase the PA network coverage to up to 30% of the landscape of the Zhangjiang River Basin for target species in the karst area of southwest China, a global biodiversity hotspot. Zonation 4GUI was used to evaluate the adequacy of current PAs and to strategically expand PAs while maximizing the coverage of target species and considering ecological integrity and socioeconomic activities. The results show that significant habitat degradation has occurred across 77.9% of the basin. The current PAs cover 6.3% of the site and represent 8.7% of the total distribution of key species. With regards to the threshold of protection of 30% of the area, protecting an additional 27.2% of the site under an ecological integrity prioritization scenario and a scenario of the socioeconomic costs involved in iteration would cover 93.5% and 80.4% of the ranges of the key species, respectively. Our results can be used to inform the upcoming actions associated with karst area conservation-related policies.