Brittle fracture initiation characteristics of a single notch or the correlation between the brittle fracture initiation temperature and the crack length at any stress levels has been evaluated by using the deep notch test specimens. However, sometime two cracks might exist in the welded joint and the distance between these notches is so small that the interference should be taken into account. In this paper, the effect of distance between twin notches or equi-length notches in a line being perpendicular to the applied stress on the brittle fracture initiation characteristics was investigated experimentally by using the wide plate test specimens with twin notches. The length of through-thickness notch was 40 and 80 mm, and the distance between two notches varied from 10 to 160 mm. The steels tested was a 60 kg/mm² high strength steel and the specimen size was 20×400×500 mm. In addition, the crack opening displacement (C. O. D.) at the inside and the outside tips of notch were measured by means of the electrostatic capacitance method which has been recently developed by the authors. The test results were compared with the theories based on the stress intensity factor and crack opening displacement. When the distance between two notches, l , is less than the notch length, 2 c , the fracture stress decreases with decreased distance, l . However, when l is small, the fracture stress increases casually with decreased distance, where the fracture stress is nearly equal to that for a single notch in a length of overall length of two notches, 2×(2 c )+ l .