This study investigated the effect of solid-state fermentation (SSF) on the phenolic enrichment in low-value grain processing by-products. Food-grade microorganisms (Aspergillus awamori, Rhizopus oryzae, Bacillus subtilis, and Saccharomyces cerevisiae) and their cell wall-degrading enzymes (amylase, cellulase, β-glucosidase and xylanase) were examined for their potential to increase the total phenolic content (TPC) of grain brans/hulls (oriental mustard bran, yellow mustard bran, wheat bran, Amarillo pea hull and Dunn pea hull) during a 7-day SSF. With the exception of Dunn pea hull, the TPC of most bran/hull samples significantly increased in SSF treatment with A. awamori, R. oryzae and S. cerevisiae. In correlation with TPC results, significant increase in enzyme activities of A. awamori and R. oryzae were observed during SSF treatment. These results indicate that SSF using fungi, with their strong cell wall-degrading enzyme activities, positively affects phenolic enrichment in low-value grain brans/hulls through the release of insoluble bound phenolics.