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Adiabatic air-water two-phase flows in a commercial plate heat exchanger were visualized by thermal neutron radiography method as a nondestructive test in order to clarify liquid distributions. Liquid distributions in a single channel and a multichannel plate heat exchanger were investigated. From the results of a single channel, it was shown that gas phase tended to flow at the center of the net-like conduit and liquid fraction at the both side was higher. However, in the case of higher gas volumetric flux above 19 m/s, liquid distributions seemed to be homogenous. Measured average void fractions were lower than those by the homogenous model. On the other hand, from the results of a multichannel, it was shown that liquid distribution into the each channel strongly depended on inlet conditions. In the case of higher liquid flow rate and lower gas flow rate, liquid fraction became higher with the deeper channel due to larger liquid momentum. However, in the case of lower liquid flow rate and higher gas flow rate, the opposite tendency of liquid distribution was observed, that is to say, liquid fraction was lower with the deeper channel.