Aims: Biochar has been used as an amendment to improve soil fertility and increase crop yield. A pot trial and incubation experiment were conducted to evaluate the effects of combined biochar and phosphate fertilizer applications on changes in soil physiochemical properties, photosynthetic parameters, and plant growth of Brassica napus L. in acidic soil.Methods: Biochar (B) was applied at rates (B0: 0%, B1: 2%, and B2: 4% w/w) to the soil, while phosphorus (P) as KH2PO4 was added at P0: 0 mg kg(-1) soil, P1: 100 mg kg(-1) soil, and P2: 150 mg kg(-1) soil. Non-amended soil served as the control (Ck).Results: The study found that the maximum photochemical quantum yield of photosystem II (Fv/Fm) and non-photochemical quenching were affected by biochar and P fertilizer treatments. The Fv/Fm was significantly lower in the Ck while the highest in B2P1. Compared to the Ck treatment, the electron transport rate and photosynthetic rate were significantly increased under the application of biochar with P fertilizer. Additionally, malondialdehyde content declined by 68.9% when biochar was added with P fertilizer treatments. Furthermore, the plant P content and plant growth parameters were significantly increased. Biochar with and without P fertilizer treatments increased soil pH significantly, compared to the application of P fertilizer alone. Water-soluble P decreased with incubation time, while Al-P decreased significantly by 69.9% and 76.4% under B1 and B2 treatments, respectively, compared to CK.Conclusion: The findings revealed a positive effect of the combined application of biochar with phosphate fertilizer on the growth of oilseed rape in acidic soil.