The photochemical behavior of quaternary ammonium salts (QA salts) with N,N-dimethyldithiocarbamate as photobase generators and the photoinitiated thermal crosslinking of poly(glycidyl methacrylate) (PGMA) with the QA salts were investigated. The formation of basic compounds in the photolysis of 1-phenacyl-(1-azonia-4-azabicyclo [2,2,2]octane) N,N-dimethyldithiocarbamate was ascertained by the color change of phenol red as an acid-base indicator. H-1 NMR spectra of photoproducts in CDCl3 under N-2 showed that the photolysis of 1-naphthoylmethyl-(1-azonia-4-azabicyclo[2,2,2] octane) N,N-dimethyldithiocarbamate resulted in the quantitative formation of triethylenediamine and a dithiocarbamate derivative. The presence of oxygen in the photolysis decreased the photolysis rate. The amine was also detected in its photolysis in polystyrene films. The effects of ammonio groups and counteranions of QA salts on the photoinitiated thermal crosslinking of PGMA films were also investigated. Quaternary ammonium dithiocarbamates acted as excellent photobase generators and effective photoinitiated thermal crosslinkers for PGMA.