Though agriculture is the mainstay of Ethiopian economy, it is suffering from many disasters.rnAmong these disasters, nutrient depletion of the soil is the major one. Applying organic and/orrninorganic (chemical) fertilizer in the soil can curb nutrient depletion. Scarcity of organicrnfertilizer, here in Ethiopia, brings about the need to use chemical fertilizer. But, still, there is arnproblem of using sufficient amount of chemical fertilizer based on initial fertility status of thernsoil and nutrient requirement of crops to bring high yield. Hence, this and others arouse interestrnof developing a guideline for fertilizer recommendation. This thesis developed a decision support system that can help agricultural researcher in thernprocess of building a guideline for fertilizer recommendation. In doing so, the research aimed tornassess the potential applicability of data mining technology specifically decision tree teclmiquernto help in fertilizer-grain yield data analysis in decision-making process. In this research, in the process of building a model, different steps were undertaken. Among thernsteps, data collection, data preprocessing and model building and validation were the majorrnones. Different tasks performed in each step are mentioned as follows. The data were collectedrnfrom National Soil Testing Center. Under preprocessing, data cleaning, discrimination andrnattribute selection were done. The final step was model building and validation and it wasrnperformed using the selected tools and techniques. The data mining tool used in this research was Weka. In this software the decision tree 148rnalgorithm was selected since it is capable to analyze numeric data. After successive experimentsrnwere done using this software, a model that can classify crop yield as high, medium and lowrnwith better accuracy to the extent of 85% and sound rule was selected. Experimental resultsrnshow that deci sion tree is a very helpful tool to depict the contribution of soil-pH, initialrnavailable so il phosphorus, organic-matter, total nitrogen and treatment to bring high tef andrnwheat yield. The reported findings are optimistic, making the proposed model a useful tool inrnthe decision making process. Eventually, the whole research process can be a good input forrnFurther in-depth research.