The aim of this study was to determine the optimal conditions for high-quality dietary fibre (DF) production by Agrocybe chaxingu in a submerged culture fermentation system of wheat bran. The substances which may affect DF quality were first selected by Plackett-Burman design, and then the D-optimal design was applied for further optimization to obtain the highest quality of DF. The results suggest that vitamin B (VB), MgSO · 7HO and yeast extract are factors that have a significantly positive effect on DF production. The highest quality of DF was obtained in a solution of 50 g wheat bran and 1 L distilled water to which 0.14 g VB, 1.10 g MgSO · 7HO and 2.50 g yeast extract had been added; 22.32 % soluble DF of the total DF amount was found. These results indicate that submerged culture fermentation of A. chaxingu is a novel and good method for producing high-quality DF.