Since it was firstly identified in Suweon during the growing season in 1986, this fungus of peanut web blotch, Phoma arachidicola, has been widely distributed to the major peanut growing areas throughout the whole country. Disease symptoms appeared on the adaxial surface of peanut like ink drop lesion with net form, and finally turned to dark brown blotch. The fungus isolated was revealed to form dark brown colonies on PD agar at $28^{circ}C$, resulting 4.5 mm mycelial extension per day. Hyaline conidia were observed to be either aseptate or single septeted, and sized with the ellipsoidal to cylindrical shape $3.0{ imes}14.5;{mu}m$. The optimum temperature was ranged 24 to $26^{circ}$ in the grwoth. Virginia type peanut was more resistant to the fungus than Spainish type in the field reaction.