Urea is extensively used as fertilizer in the agricultural industry based on its suitability for all types of crops. The hydrolysis of urea fertilizer produces ammonia (NH3) and carbon dioxide (CO2). However, up to 40 of NH3 release affects the efficiency of urea fertilizer. By introducing inhibitors into the urea enzymatic reaction, the NH3 emission problem can be solved. Unfortunately, current inhibitors are usually chemical based and non-biodegradable. Several complaints and accidents have been reported when handling chemical based inhibitors especially for surface application. Research on garlic or Allium savatium has been conducted to ensure its inhibitory effects as potentially safe and biodegradable inhibitor. From previous research, thiosulfinates (TS) contained in garlic extract proved to inhibit platelets aggregation in medical applications. In this study, the inhibitory effect is determined by analyzing NH3 concentration in urease-garlic mixture and standard urea assay mixtures using UV-VIS spectrophotometer device. Previous research showed the highest absorbance of free NH3 was detected at 370nm. At 30 minutes of 15ml of urease-garlic mixture confirms the fully inhibition of garlic extract towards reaction. Copyright © 2014 Trans Tech Publications Ltd, Switzerland.