Objectives: Carbon nanotubes (CNTs) are allotropes of carbon with a length-to-diameter ratio greater than 106 with the potential uses as medical diagnostic or therapeutic agents. In vitro studies have revealed that gadolinium (Gd) nanoparticle-catalyzed single-walled carbon nanotubes (SWCNTs) possess superparamagnetic properties, which enable them to be used as contrast agents in magnetic resonance imaging (MRI). Our study synthesized Gd-CNT for use as MRI contrast agents. Methods: To reduce the toxicity and solubility of CNTs, it was functionalized, and after loading with Gd was coated with polyethylene glycols (PEG). We then synthesized different concentrations of Gdn3+@CNTs-PEG and Gadovist® to be evaluated as MRI contrast agents. Results: The analysis showed that the Gd concentration in Gadovist® was 12.18% higher than synthesized Gdn3+@CNTs-PEG, but the mean signal intensity of the Gdn3+@CNTs-PEG was approximately 3.3% times higher than Gadovist®. Conclusions: Our findings indicate that synthesized Gdn3+@CNTs-PEG has the potential to be used as an MRI contrast agent in vitro, but in vivo assessment is necessary to determine the bio-distribution, kinetic, and signal enhancement characteristics.