In a method of testing an interconnection substrate, a blocking condition of a reference light reflected from a probe having an intrinsic optical characteristic may be set. An electric field emitted from a test interconnection substrate having a plurality of circuits may change the intrinsic optical characteristics of the probe into test optical characteristics. Light may be irradiated to the probe having the test optical characteristics. The reference light reflected from the probe having the test optical characteristic may be blocked in accordance with the blocking condition. The remaining reflected light that may be due to an abnormal circuit may be detected.