Micropatterns of a SnO2 thin film were obtained by lithographic photoirradiation followed by pyrolysis of thin films of an organotin polymer poly(4-((trimethylstannyl)methyl)styrene) (1). Irradiation of the polymer thin film by a KrF laser through a photomask followed by development gave a negative pattern of the insolubilized polymer. The following pyrolysis afforded a pattern of SnO2 without significant deformation of the pattern except for a reduction of the film thickness. The pyrolysis of the irradiated film without the development also gave a negative pattern of SnO2. The cross-linking of the organotin polymer caused by the irradiation was necessary both for lithographic processing and for SnO2 formation. In the conversion of the polymer to SnO2 during the pyrolysis, the cross-linked network seems to encapsulate low molecular weight intermediates, preventing their escape from the polymer film.