<p>Global warming and human activities have reduced the concentrations of dissolved oxygen in the bottom water of lakes, resulting in increased anoxia in surface sediments. This increased anoxia likely alters carbon cycling processes (e.g., organic carbon mineralization) by altering microbial community composition and functions in lakes. However, it remains unclear how organic carbon mineralization responds to increased anoxia in surface sediments of lakes (particularly saline lakes). In this study, CO₂ production in surface sediments of six lakes with different salinity (0.47–250 g/L) on the Tibetan Plateau was investigated using microcosm incubations under aerobic and anaerobic conditions, respectively, followed by geochemical and microbial analyses. The results showed that for the freshwater lake, CO₂ production rates in anaerobic sediment microcosms were significantly (<i>P</i> &lt; 0.05) lower than their aerobic counterparts. In contrast, an opposite trend was observed for CO₂ production in saline lakes. Furthermore, the CO₂ production rates decreased significantly (<i>P</i> &lt; 0.05) under aerobic conditions, while it exhibited a hump-like relationship with increasing salinity under anaerobic conditions. Taken together, our results suggest that increased anoxia would enhance organic carbon mineralization in surface sediments of saline lakes and help understand carbon feedback on global changes in saline lakes.</p>