Study on effect of compost on mycorrhizal fungi change and super sweet corn yield in Mapbon soil series was conducted at Land Development Station, Rayong Province during 1994 - 1997. Completely randomized block design was planned which consist of applicated compost 0, 2, 4 and 6 ton per rai and chemical fertilizer (15-15-15) 0 and 25 kg. per rai. There were 8 treatments in 3 replications. The results had shown that addition compost 4 to per rai had effect increasing bacterial number in soil after harvesting corn yield from 7.51 to 8.85 log no. per gm soil. Chlamydospore of mycorrhizal fungi was increase from 13.9 to 35.4 spore per 100 gm soil and vesicle number in fibrous root cell also raised from 56 to 79 cells per 5 pieces of root cell which had relation to the increment of available nutrient in soil Phosphorus, potassium, calcium, magnesium and sulphur were increase from 8.5, 46, 66, 7.1 and 7.5 to 15.9, 64, 109, 19 and 9.8 ppm respectively. Addition compost 6 ton per rai with chemical fertilizer gave the highest corn yield from 3,633.3 to 4,233.5 kg per rai.