Three kinds of phthalocyanine (Pc) thin film solar cells, i.e. ITO/Pc/Al, ITO/Pc/In and Al/Pc/Au were fabricated and effects of NO2 gas on their photovoltaic performance were investigated. The introduction of NO2 gas was confirmed to influence the electronic behavior of the cells both in darkness and under illumination. Adsorbed NO2 gas was suggested to work as an electron acceptor for Pc and improved the photovoltaic performance. However, chemical reaction between the metal electrode and NO2 formed some oxide and deteriorated the Schottky barrier, resulting in an increase in cell resistivity. The cell deterioration was delayed somewhat in ITO/Pc/In cells, since the electrode indium has higher oxidation resistance than aluminum. The cell of Al/Pc/Au structure may utilize sufficiently both photovoltaic and NO2 gas adsorption effects.