Agricultural by-products can be converted into organic fertilizers through thermophilic composting process. In this study, four combinations of different agricultural by-product materials were composted to find a mixing treatment that improves thermophilic composting process and produces good quality compost. Four treatments included M1 (straw, chicken manure, elephant grass), M2 (straw, chicken manure, cabbage leaves), M3 (straw, cow manure, elephant grass) and M4 (straw, cow manure, cabbage leaves). Compost phytotoxicity was tested on Brassica and Spinach seeds through germination tests. Experiment of evaluating the effects of those compost combined with inorganic nitrogen fertilizer on the growth and yield of cucumber were also conducted. Research results indicate that using agricultural by-product composting materials including straw, chicken manure with elephant grass or cabbage leaves gave better temperature behavior, compost quality and volume than others. Composts of the treatments are considered free toxicity because they all give a germination of over 80%. Applying 70% composts of M1 or M2 combining with chemical nitrogen fertilizer replaced for 30 % of nitrogen in compost to soil increased significantly the growth and yield of cucumber. The agricultural by-products thus should be converted into nutritious compost which is healthy food feeding soil and crops to contribute to close the food chain in circular agriculture, protect environment, develop agriculture production sustainably.