Brachytherapy is one of the important methods of cancer treatment. The dosimetry characterization should be performed before any possibility of the new sources is used at a clinical stage. Monte Carlo methods are best to calculate the dosimetry parameters of the radioactive sources. Therefore, dosimetry parameters of beta-emitting Pr-142 radioactive source were evaluated according to the recommendations of AAPM TG 43 and TG 60 using MCNP5 code. Reference dose rate, geometry function, radial dose function, and anisotropy function were calculated for Pr-142 brachytherapy seed. Beta particles from Pr-142 source have short-range and this prevents to damage the healthy tissue. Hence, Pr-142 is suitable for superficial tumors like eye cancer. As a result, eye geometry was simulated and the dose distribution of Pr-142 radioactive seed was determined using with MCNP5 code to develop a brachytherapy treatment for eye cancer.