The purpose of this research was to improve the diamond post-mining soil quality using a bioremediation composting method based on the cow manure and organic waste from a traditional market. This research was conducted for: 1) identifying the conditions for temperature, pH and moisture during the composting process; 2) analyzing the difference of variations in composition and the best composting durations. The bioremediation method used is open windrow composting, divided into four composition variations, namely variation A (100% soil); B (75% soil: 25% compost); C (50% soil: 50% compost); D (25% soil: 75% compost). The variations of composting duration are 15th and 30th days. From the result of two-way ANOVA test, it can be concluded that there is no significant difference in the decrease of Fe value due to the variations in composition ratio and duration of composting.