We describe the sound emission board proposed for installation in the acoustic positioning system of the future KM3NeT underwater neutrino telescope. The KM3NeT European consortium aims to build a multi-cubic kilometre underwater neutrino telescope in the deep Mediterranean Sea. In this kind of telescope the mechanical structures holding the optical sensors, which detect the Cherenkov radiation produced by muons emanating from neutrino interactions, are not completely rigid and can move up to dozens of meters in undersea currents. Knowledge of the position of the optical sensors to an accuracy of about 10 cm is needed for adequate muon track reconstruction. A positioning system based on the acoustic triangulation of sound transit time differences between fixed seabed emitters and receiving hydrophones attached to the kilometre-scale vertical flexible structures carrying the optical sensors is being developed. In this paper, we describe the sound emission board developed in the framework of KM3NeT project, which is totally adapted to the chosen FFR SX30 ultrasonic transducer and fulfils the requirements imposed by the collaboration in terms of cost, high reliability, low power consumption, high acoustic emission power for short signals, low intrinsic noise and capacity to use arbitrary signals in emission mode. ; European Commission [DS 011937 ; 212525] ; Ministerio de Ciencia e Innovacion (Spanish Government) [FPA2009-13983-C02-02 ; ACI2009-1067 ; CSD2009-00064] ; Generalitat Valenciana [Prometeo/2009/26] ; Llorens Alvarez, CD.; Ardid Ramírez, M.; Sogorb Devesa, TC.; Bou Cabo, M.; Martínez Mora, JA.; Larosa, G.; Adrián Martínez, S. (2012). The sound emission board of the KM3NeT acousticpositioning system. Journal of Instrumentation. 7(1):1-9. doi:10.1088/1748-0221/7/01/C01001. ; Senia ; 1 ; 9 ; 7 ; 1