This study aimed to developed radiolabeled methotrexate (MTX) loaded nanoparticulate systems for breast cancer imaging. For this aim, two formulations (F1 and F2) of MTX loaded chitosan nanoparticles (CSNPs) were prepared via ionic gelation process by using CS and tripolyphosphate (TPP). The obtained results showed that by using F1 and F2 formulations with mean diameter of 169.000 nm and 427.633 nm, zeta potential of 20.133 mV and 29.067 mV were successfully developed with ionotropic gelation process and the encapsulation efficiency (EE) of F1 and F2 was found nearly 35% and 64% respectively.In addition, MTX-CSNPs were radiolabeled by Technetium-99m (99mTc) and radiochemical purity and stability of labeled compound were performed using a gamma counter up to 6 h. Results indicated that MTX-CSNPs were radiolabeled by 99mTc with high labeling efficiency (>90%) and stability.For in vitro incorporation studies the uptake differences between 99mTc labeled MTX loaded and unloaded CSNPs, reduced/hydrolyzed (R/H) 99mTc were evaluated in human breast cancer (MCF-7) and human keratinocyte (HaCaT) cell lines. According to cell culture studies, the incorporation percentages of 99mTc-MTX-CSNPs were highly uptake in cancer cell line. The results demonstrated that radiolabeled MTX-CSNPs may be a promising agent for breast cancer diagnosis.