The composition of the aerosol from the ozonolysis of cyclohexene in the absence of seed particles has been investigated by laboratory chamber experiments. The aerosol collected on filters was analyzed by a liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry. Low-molecular weight products, i.e., dicarboxylic acids, oxocarboxylic acids, and hydroxydicarboxylic acids, as well as oligomers with molecular weights more than 200 were found in the aerosol.