Effects of film thickness and crystal morphology on the gas sensing characteristics of a chemiresistor-type NO2 gas sensor based on the lead phthalocyanine thin film are investigated in this work. We found that the monoclinic PbPc film has the highest steady-state sensor current, followed by the amorphous film and the triclinic film. This can be explained by variations in the conduction path and the number of adsorption sites among the different crystal morphologies. The amorphous film also has the fastest response time and recovery time due to its looser molecular stacking and more porous structure. The least porous triclinic PbPc film has the slowest response characteristics. Steady-state current, response time and recovery time all increase with the film thickness, and reach their maximal values at a limiting thickness. The limiting thickness is 300 nm for the triclinic film, 600 nm for the monoclinic film and 700 nm for the amorphous film.