Photodecomposition processes of 2-, 3-, and 4-methylaniline cations induced by a moderately intense (similar to 10(11) W/cm(2)) visible nanosecond laser field and an intense (similar to 10(15) W/cm(2)) UV femtosecond laser field have been investigated using a tandem mass spectrometer. Highly unsaturated fragment cations such as C6H2+ and C6H3+ are dominantly produced by the nanosecond laser, while less unsaturated smaller fragment cations such as C3H3+, C4H4+, and C5H5+ are produced mainly by the femtosecond laser. Ab initio calculations have also been performed to estimate the stable geometrical structures of C6H2+ and C6H3+ and those of possible intermediate ring compounds for discussing the photodecomposition pathways in intense laser fields. (C) 2008 Elsevier B. V. All rights reserved.