The roles of fungal diseases in the decline of standing milk-vetch pastures were investigated in field plot and glasshouse experiments in Gansu Province, China. Experimental plots within 8-, 6-, 4- and 3-year-old stands were used for measurement of plant populations and productivity, and to survey the mycobiota of root, stem and foliage tissues of healthy plants and diseased plants (showing symptoms of yellow stunt and root rot disease). Selected fungal isolates were tested for pathogenicity by inoculating 2-day-old seedlings grown in pots of sterilised soil. Plant mortality increased and plant density and productivity decreased progressively with age of stand. Of the 27 fungal species of 21 genera isolated from field-grown plants, the most frequently isolated from roots were Fusarium chlamydosporum and F. solani (other Fusarium spp. were also common), whereas Embellisia sp. and Alternaria sp. were most common from aerial tissues of diseased plants. The 11 species tested for pathogenicity could be divided into four virulent types: strongly virulent (Embellisia sp.), moderately virulent (F. oxysporum, F. chlamydosporum and F. avenaceum), weakly virulent (F. solani, F. semitectum, F. verticilloides, Conostachys rosea and Cladosporium herbarum) and non-virulent (Alternaria alternata and Alternaria sp.). Root rot caused by Embellisia sp., together with Fusarium spp. and C. rosea, appears to be the main fungal disease contributor to decline of standing milk-vetch pasture in northern China.