Electrical conductivity of a single crystal of (TTF)18(I3)18(CH2Cl2)2 was measured under high pressure up to 20kb. At ambient pressure, the conductivity was semiconducting but an anomalous deviation from the linearity in its log σ vs. 1/T curve at about 220K. This knee was suppressed by applying pressure. Furthermore another conductive deviation was observed around room temperature under 20kb. The results are discussed in terms of two phase transitions. © 1991.