We present BeppoSAX observations of the starburst/Seyfert composite galaxy Mrk609 .
This enigmatic object has an optical spectrum dominated by the features of starburst galaxies , yet its X-ray luminosity ( 6.3 \times 10 ^ { 42 } { erg s ^ { -1 } } ) is typical of an AGN .
The X-ray spectrum of Mrk609 can be parameterised by a single power-law model with a photon index \Gamma \sim 1.6 \pm 0.1 and no evidence for significant absorption above the Galactic value .
Long term variability in both the 0.1-2 keV and 2-10 keV energy bands is detected , again suggesting that the X-ray emission is dominated by an AGN .
The observed broad Ha component is a factor of 40 below that predicted by the X-ray flux implying a deficit of ionizing UV photons .