Steel slag is a by-product in the process of refining iron by Blast Furnace (BF) or Electric Arc Furnace (EAF). This by-product can be used for various fields such as construction, industry and agriculture. This study aimed to observe the use of steel slag in agriculture as fertilizer, lime and ameliorant in the soils. The method used was the experimental design used steel slag in several level: 1,2,3,4,5,6,7,8 to 9% to change several soils characteristics of Ultisols and Andisols. The result showed that steel slag increased pH, decreased P=fixation and P-retention and increased available P ini Ultisols and Andisols. This result of this research is expected contributed to government who would like to improve characteristics in sub optimal soils. The novelty is the using of steel slag in agriculture that not been used widely yet.