Slaughterhouses are known as places to produce meat for human consumption. On the other hand, slaughterhouses produce livestock waste, one of which is rumen. The rumen's high nutrient and microbial content provide an excellent opportunity for its use as liquid organic fertilizer for plant growth and development. However, evaluation of rumen addition concentration during the manufacture of liquid organic fertilizer is still scarce and needs to be carried out. Therefore, this research aims to obtain a suitable rumen addition formulation for making liquid organic fertilizer. Rumen waste was varied in 4 concentrations, namely 20%, 40%, 60% and 80%. Supporting ingredients, such as laos, ginger, turmeric, galangal, and rice washing water, are mixed with the rumen, which is then incubated for 15 days to obtain liquid organic fertilizer. Analysis of total nitrogen content, C/N ratio, total phosphate, total potassium, total microbes, and physical characteristics was carried out to evaluate the quality of liquid organic fertilizer. The results showed that the addition of 80% rumen was able to play a role in producing liquid organic fertilizer with high total nitrogen (2.35%), low C/N ratio (6.05), high total phosphate (1.19%), and high total potassium (1.75%). Furthermore, liquid organic fertilizer made with the addition of 80% rumen contains high total microbes (5.5 x 1010 CFU/mL), is bright brown, yellowish in color, and has an earthy aroma. This research indicates that adding 80% rumen can produce good quality liquid organic fertilizer. This information can be the basis for further research regarding the rumen potency as an ingredient of organic fertilizer.