Bio-ash is produced from burning of biological solid waste, high in porosity, large in water absorption capacity, comprehensive in nutrient, sterile and non-toxic. An indoor incubation experiment was carried out using ashes of sawdust, rice husks, rice straws and corn stalks to explore effects of the ashes, when mixed at a varying ratio with chemical fertilizer on N volatilization from the fertilizer within a certain time period. N volatilization was determined with the alkali absorption method. Results show that the mixtures of the four kinds of ashes and chemical fertilizer regardless of N level (N1, N2 and N3), with the time going on, N volatilization increased first and then declined in both volume and rate, with peaks mostly appearing on D10~D15 of the incubation. In the mixture of rice husk ash, corn stalk ash and rice straw ash, addition of potassium dihydrogen phosphate significantly enhanced the effect of inhibiting volatilization of ammonia, while in the mixture of sawdust ash, the addition of potassium chloride or potassium dihydrogen phosphate had the same effect. Among the four kinds of ashes, sawdust ash was the lowest in the effect of inhibiting volatilization of ammonia. Therefore, ammonia volatilization was much higher in the mixture of sawdust ash than in the other three, and even reached as high as 5 times that of the others, especially, the mixtures were at N3 level. The effect of sawdust ash (pH12.8) varied with N level, displaying an order of N1 > N2 > N3. Elovich equation and parabolic diffusion equation can be used to fit the volatilization of ammonia from the mixtures over time, with correlation coefficients reaching an extremely significant level.