Abstract: Microplastic pollution is common in farmland soils that have been mulched for a long time, and reducing the environmental harm caused by this pollution is necessary. Biochar is widely used as a soil amendment, and its regulatory effect on microplastic pollution is still unclear. To address this, treatments with 2% polyethylene (PE) microplastics (traditional microplastics), 2% polylactic acid (PLA) microplastics (biodegradable microplastics), 2% biochar (BC), 2% polyethylene + 2% biochar (PE+BC), 2% polylactic acid + 2% biochar (PLA+BC) and a control (no microplastic or biochar, CK) were used to compare the effects of biochar on nutrients, bacterial communities and functions of soils contaminated with these two types of microplastics in this study. The results revealed that: (1) Soil nutrient content decreased in response to both types of microplastic pollution and the addition of biochar alleviated the negative effects of microplastic pollution on soil nutrients. At the end of the 70-day incubation period, compared to CK treatment, the contents of soil available nitrogen (AN) and available phosphorus (AP) in the PE treatment had significantly decreased by 4.4% and 8.2%, respectively, while the contents of AN and AP in the PLA treatment decreased by 3.3% and 3.4%, respectively. However, there was no significant difference in nutrient contents between the PE treatment and PLA treatment. The contents of AN, AP and AK in the PE+BC treatment and PLA+BC treatment were significantly greater than those in the PE and PLA treatments (P<0.05). (2) The relative abundances of some important bacterial phyla and genera were significantly reduced by microplastic pollution, but the addition of biochar could alleviate this effect. At the end of incubation, the relative abundance of Actinobacteria in the PE, PLA, PE+BC and PLA+BC treatments had significantly decreased by 58.6%, 52.8%, 31.5% and 39.8%, respectively, compared with that in the CK treatment. The reduction in the relative abundances of Actinobacteria in the PE+BC treatment and PLA+BC treatments was significantly less than those in the PE and PLA treatments (P<0.05). In addition, compared with that in the CK treatment, the relative abundance of Sinomonas in the PE treatment was significantly lower by 31.8%, and the relative abundance of Sphingomonas in the PLA treatment was significantly lower by 40.0%. The relative abundances of these two bacterial genera, known for promoting plant growth, were significantly greater in the PE+BC treatment and PLA+BC treatment (P<0.05). (3) The relative abundances of several functional genes related to carbon cycle were significantly reduced by microplastic pollution, and the addition of biochar could change this effect. At the end of incubation, the relative abundances of functional genes associated with methanol oxidation, methylotrophy, chemoheterotrophy, and aerobic chemoheterotrophy were significantly lower in the PE, PLA, PE+BC, and PLA+BC treatments than those in the CK treatment (P<0.05). The decrease magnitude in the relative abundances of functional genes associated with chemoheterotrophic and aerobic chemoheterotrophy in the PLA+BC treatment was significantly less than those in the PLA treatments. The relative abundances of functional genes associated with methanol oxidation and methylotrophy in PE+BC and PLA+BC treatments were significantly greater than those in PE and PLA treatments. This research shows that soil nutrient content decreases and bacterial community structure and function are negatively affected by both traditional microplastic and biodegradable microplastic pollution and the effects of these two types of microplastic pollution are different. The addition of biochar can alleviate the negative effects of these two types of microplastic pollution on soil.