Nitrogen loss via ammonia volatilization during the early period of composting process decreases N concentration in the final compost, leading to imbalance between N/P in the compost and crop requirement of N/P. Application of compost at the rate to meet crop requirement of N freqently resulted in accumulation of soil P. Therefore, it is urgent to develop composting techniques to reduce ammonia volatilization loss. Understanding of the ammonia volatilization patterns as affected by co-existed organic matter added to manure for enhancement of composting process may be helpful in developing such composting techniques. In this study, we investigated the effect of different organic amendment in terms of biodegradability on ammonia volatilization during 4 weeks of composting in a continuous-flow experiment. Either sawdust (SD, low biodegradability) or rice bran (RB, high biodegradability) was mixed with cattle manure at a various rate. Emitted CO₂ and NH₃ were collected and periodically determined. Percentage of dry matter loss during the composting period was also calculated. The amount of CO₂ emitted was much higher in the RB treatment than in the SD treatment. Accordingly, % of dry matter loss ranged from 35.1~41.5% in the RB treatment and that from 18.7~22.6% in the SD treatment. Such pattern clearly showed that RB is more biodegradable than SD. During the early composting period up to 8 days, negligible amount of ammonia volatilization was detected in both treatment regardless of the amendments. No meaningful ammonia volatilization was detected in the SD treatment until the end of composting. In the RB treatment, however, significant amount of ammonia volatilization was observed thereafter. Such differences could be attributed to the different properties of SD and RB. For example, the high C/N ratio of SD could enhance NH₄ ⁺ immobilization and thus decrease NH₄ ⁺ concentration that is susceptible to ammonia volatilization. Binding of NH₄ ⁺ on to phenolic compounds of SD may also contribute to the decrease in NH4 + concentration. Meanwhile, as RB has a relatively low C/N ratio, remineralization of immobilized NH₄ ⁺ could increase NH₄ ⁺ concentration as high as the level for the occurrence of ammonia volatilization.