This study was conducted to investigate the effect of swine liquid manure(SLM) and phosphorus fertilizer from September, 1998 to July, 1999 on the soil fertility on Italian ryegrass field, Cheju volcanic ash soil. pH(lst investigated), Mg (2nd investigated) and Cu content (2nd investigated) on soil grown by Italian ryegrass were significantly increased by an increase of fertilizer P(P<O.O5). Pig liquid manure application increased significantly pH(1 st), OM(l st), Mg(2 nd), C/N ratio(1 and 2nd) and Cu(1 st and 2nd) content in soil(P<O.O5). There was significantly an interaction in Ca(2nd), Mg(2nd) and Cu(2nd)contents of the soil grown by Italian ryrgrass between fertilizer P and pig manure (P<0.05). Number of bacteria-in the field soil of Italian ryegrass was higher in no manure than manure application level, while number of fungi was not revealed the effect of fertilizer P and swine liquid manure. It can be concluded that the available phosphorus content in the soil did not get the effect of fertilizer P and swine manure application because of soil erosion by high rainfall and low P fertilizer application for avoiding large phosphorus runoff under high rainfall is required and swine-liquid manure applied with P fertilizer is effective for improvement of 1 physical and chemical soil properties for over-winter Italian ryegrass. (Key words : Italian ryegrass, Phosphorus, Swine liquid manure, Volcanic ash soil)