Among the tokamaks in the world, DAMAVAND is one of the small ones and, regarding the features of its plasma, offers useful and important research fields among which the plasma heating injector design is one of the most conspicuous ones. The heart of any neutral beam injector is the ion source in which ions are produced for the first time. In this paper, conceptual design of an ion source for plasma heating in DAMAVAND tokamak is presented. The machine is based on positive ion injection. Compelling reasons for the selection of this type of source are mentioned. Further, in this paper, we investigated different types of suitable ion sources for plasma heating in tokamaks. Therefore the bucket ion source is selected. Then, the conceptual design of a bucket ion source used in DAMAVAND-NBI has been elaborated upon. It is shown that taking the tokamak parameters and the amount of beam absorption into consideration, the bucket ion source must deliver a beam with 4.5 keV, 30.15 kW and 6.7 A, which are critical energy, neutral beam power, and neutral beam current respectively, required for DAMAVAND tokamak plasma heating.