【Objective】 The objective of this study is to discuss the effect of intracellular DHN melanin of Setosphaeria turcica on the appressorium turgor pressure generated and elucidate the invasive mechanism of S. turcica. 【Method】 In this research, the best conditions for appressorium formation of S. turcica were determined by inducing appressorium production. The appressorium cell wall pore sizes and turgor pressures of wild-type isolate 01-23 and melanin-deficient strains △St3hnr of S. turcica were measured by a solute exclusion technique and incipient-cytorrhysis technique. 【Result】 The appressorium pore size of wild-type isolate 01-23 was 2.1-2.7 nm and it had a 5.4 MPa turgor pressure, while it was shown a range of 2.7-3.3 nm in melanin-deficient strains △St3hnr and a lower pressure about 4.1 MPa. The results indicated that appressorium without melanin could not form a high turgor pressure resulting in losing the ability for penetrating. 【Conclusion】 It is suggested that the melanin layer is significant in accumulation of excess turgor pressure and the turgor pressure of S. turcica play a major role in substance penetration.