Asymmetrical phthalocyanines are seldom applied to gas sensor field because of its difficulties in synthesis, but asymmetrical phthalocyanines possess donor or acceptor substituents in its peripheral ring, thus have many advantages over symmetrical phthalocyanines. Aminotri-tert-butylphthalocyanine (AmBuPc) is a new asymmetrical phthalocyanines, which possesses three tertbutyl groups and one amino group that both are electron-donating substituents; this paper reports its vacuum evaporated thin films gas sensitivity in 4.1 x 10(-5) kg/m(3) nitrogen dioxide environment. The gas sensor appears good gas sensitivity to nitrogen dioxide and a linear relationship between log (resistance) and log (NO, concentration) was observed. A possible interaction mechanism between NO2 and AmBuPc was reported using UV-Vis, IR, SEM and XPS.