The negative ion photoelectron spectrum of AsO- has been measured, assigned, and analyzed. The adiabatic electron affinity, EA(a), was determined directly from the photoelectron spectrum. The dissociation energy of AsO-, D-0(AsO-), was computed via an energetic cycle using our measured value of EA(a) and existing literature values for other necessary quantities. Franck-Condon analysis provided values for the bond length of the AsO- anion, r(e)(AsO-), its vibrational frequency, omega(e)(AsO-), and its anharmonicity constant, omega(e)chi(e)(AsO-). The values of the molecular constants which were determined in this work are : EA(a)(AsO) = 1.286 +/-0.008 eV, D-0(AsO-) = 4.74 +/- 0.08 eV, r(e)(AsO-) = 1.696 +/-0.010 Angstrom, omega(e)(AsO-) = 827 +/- 40 cm(-1), and omega(e)chi(e)(AsO-) = 5.54 cm(-1). In addition, we determined the X (3)Sigma(-)-a(1)Delta, ground-to-first excited state splitting in AsO- to be similar to 0.54 eV.