Here we report the synthesis of boron nitride nanotubes (BNNTs) via a chemical vapor deposition method, as potential agents for boron neutron capture therapy. BNNTs were functionalized with PAMAM[G-2] dendrimer and then, conjugated with L-Phe using EDC/NHS. After that, BNNTs were radiolabeled with I-125/131, which are commonly used for both therapy and diagnosis in clinical and pre-clinical studies. BNNTs were radiolabeled with a maximum yield with I-125/131 in compared with 4-borono-L-phenyalanine which is currently used as a commercial drug. Radiolabeling parameters were optimized with thin layer radiochromatography and high performance liquid radiochromatography. BNNTs are promising nanobioconjugates as new theranostic agents.