This paper deals with evaluation of the practical significance of soil available Mn (DTPA-Mn) and the discussion of critical level.Pot and field experiments for the response of crops to manganese fertilizer on 18 loessial soils in which DTPA-Mn ranged from 1.6-25 ppm were conducted.Results of experiments showed that the content of soil available Mn (DTPA-Mn) was signifieantly positively correlated with dose of manganese fertilizer,Mn concentration of crops,amount of Mn absorbed by crops and the content of easily reducible Mn in soil.Among soil chemical properties the content of available Mn extracted by DTPA solution was the most important factor that influeneed the effect of manganese fertilizer.The lower the amount of available Mn in soil,the better the response of the crop to manganese fertilizer.For this reason it is considered that the level of soil available Mn extracted by DTPA solution may indicate the supplying capacity of manganese in soil,and consequently it may be used as the index of available Mn in soils of loess region.The soil DTPA-Mn has been divided into four levels in accordance with the response of craps to manganese fertilizer,i.e.the very low level df 4.8 ppm,the low level of 4.8-7.0 ppm,the medium level of 7.0-9.2 ppm and the high level of 9.2 ppm.The critical level of sail DTPA-Mn varied with different crops and soils.It ranged from 5.5-7.5 ppm for different craps anti 5.8-8.6 ppm for different soils.It is suggested that 7 ppm and 7-9 ppm might be used as the critical level and the range of critical levels for the soils under general condition,and 5 ppm and 5-9 ppm for the soils with lower fertility.