The present invention relates to a reducing agent for reducing odor-causing substances derived from livestock excretions, having a water-soluble silicate mixed with nano size silicate particles as an active ingredient in which the reducing agent is added when disposing livestock excretions, to reduce odor-causing substances, such as ammonia, hydrogen sulfide or the like and to allow the livestock excretions to be rapidly recycled as a resource. The reducing agent which is mixed with livestock excretions to reduce odor generated from the livestock excretions, is characterized by including 8 to 60 weight % of silicate mixture in which 5 to 20 weight 5 of nano-particulate silicate and 10 to 40 weight % of water soluble silicate solution are mixed. The reducing agent has effects capable of very effectively reducing odor-causing substances, such as ammonia, hydrogen sulfide or the like generated in recycling process of livestock excretions (composting/liquid fertilizer), and very effectively reducing odor-causing substances, such as ammonia, hydrogen sulfide or the like generated in composting and producing of a liquid fertilizer by adding an oxygen-based oxidizing agent, a chlorine-free oxidizing agent, zeolite and activated carbon to the water soluble silicate solution mixed with nano-particulate silicate. Also, the reducing agent may promote the fermentation and humification grade of livestock excretions to shorten the recycling period, and since silicate is mixed in the compost/liquid fertilizer, silicate and compost may be fertilized together by one time fertilization. [Reference numerals] (1) 5 Weight %； (2) 10 Weight %； (3) 15 Weight %； (4) 75.9 Weight %； (AA) Stir during 30 minutes 60 times per hour； (BB) 2 weight % of oxide-based oxidizing agent； (CC) 0.1 weight % of oxide-based oxidizing agent stabilizer； (DD) 1 weight % of chlorine-free oxidizing agent； (EE) 1 weight % of zeolite； (FF) 5 weight % of active carbon나노규산입자가 혼합된 수용성 규산을 유효성분으로 한 가축분뇨 유래 악취유발물질 저감제는
