Ammonia (NH3) volatilization is a major pathway for gaseous nitrogen loss from fields applied with manure. To explore effects of topdressing of bio-digested manure slurry on ammonia volatilization, a field experiment was carried out in a vegetable greenhouse, applying bio-digested pig manure slurry (DPS) on winter vegetable, cress (Oenanthe clecumbens L.) and crown daisy (Raphanus sativus L. Var. Radiculus pers.), and summer vegetable, pak choi (Brassica chinensis L.) and chrysanthemum (Chrysanthemum carinatum Schousb.). The topdressing rates of nitrogen were 72 kg hm^-2, 54 kg hm^-2, 42 kg hm^-2 and 63 kg hm^-2, respectively, during the growing periods of vegetables. Results showed that (1) topdressing of DPS led to explosion of ammonia volatilization within 48 h; (2) the accumulative ammonia release of the growing season reached 8.68 kg hm^-2 and 9.90 kg hm^-2 in cress and radish fields, respectively, which were significantly higher than those in the plots topdressing with chemical fertilizer (CF) (4.06 kg hm^-2 and 5.59 kg hm^-2); however, in the pak choi and crown daisy fields, the value was 10.40 kg hm^-2 and 11.61 kg hm^-2, respectively, which were not so significantly higher than those in the plots topdressing with CF (9.81 kg hm^-2 and 10.09 kg hm^-2); (3) ammonia volatilization contributed 11.7% and 17.7% to the total N loss, respectively in the cress and radish plots topdressing with DPS in winter, and 23.3% and 26.8% in the pak choi and crown daisy plots in summer. The former was significantly lower than the latter; (4) temperature, water content, content of soluble organic carbon, form and concentration of nitrogen, biomass and activity of microbes in the surface soil at 0～10 cm depth were found to be the main contributors to ammonia volatilization. Application of bio-digested manure slurry in the vegetable field increased nitrogen loss through ammonia volatilization from DPS per se and its stimulative effect on decomposition of soil organic nitrogen. It is, therefore, essential to pay adequate attention to effects of temperature and application method in using bio-digested manure slurry as a soil amendment.