Biochars were prepared from wastewater sludge and peanut straw using a pyrolysis method. Amelioration effects of the biochars, steel slag and steel slag combined with biochars on red soil acidity were investigated. Results indicated that steel slag and the biochars contained alkaline substances and incorporation of steel slag and biochars neutralized soil acidity, increased soil pH and soil exchangeable base cations and decreased soil exchangeable aluminum. At the end of 90d incubation, soil pH increased by 1.10, 0.72 and 0.48 units due to the incorporation of peanut straw char, steel slag and wastewater sludge char. Steel slag combined with peanut straw char had greatest ameliorating effect on soil acidity, and led to soil pH increased by 2.14 units, while the amelioration of the biochar generated from wastewater sludge on soil acidity was lowest. Steel slag and biochars contain some nutrients and addition of steel slag and biochar can improve soil fertility. Among the treatments of steel slag, peanut straw char, biochar from wastewater sludge, incorporation of steel slag obtained the greatest increase in soil exchangeable Ca2+ due to the highest content of Ca in it, and soil exchangeable Ca2+ was 4.5 fold higher than that of control. Incorporation of peanut straw char increased soil exchangeable K+ greatly, and soil exchangeable K+ was 7 folds higher than that of control. Incorporation of biochar from wastewater sludge led to greatest increase in soil available phosphorus due to the highest content of P in it and soil available phosphorus was 5.4 folds higher than that of control. Both slag and biochars increased soil exchangeable Mg2+ significantly, and higher increase in soil exchangeable Mg2+ was obtained by combination of steel slag with biochars. Therefore, incorporation of steel slag combined with biochars not only neutralized soil acidity, but also increased contents of some soil nutrients because of variation of steel slag and biochars in alkalinity and nutrient contents.