The development of magnetic resonance imaging (MRI) contrast agents with high sensitivity and good biocompatibility is of great value for the diagnosis of primary hepatocellular carcinoma (HCC). Here, a novel MRI contrast agent based on calcium phosphate (CaP) nanoparticles modified with a liver cancer cell targeting peptide A54 (A54-CaP) was fabricated. The T1-positive contrast agent Gd-DTPA was encapsulated inside the nanoparticles (A54-CaPNPs), with a mean diameter of 30 nm and a high encapsulation efficiency of 92.73%. The A54-CaPNP solution exhibited higher longitudinal relaxivity (6.07 mM-1 s-1) than that of the clinically used MRI contrast agent Gd-DTPA (3.56 mM-1 s-1). A much higher accumulation of the nanoparticles in the liver cells was observed, which was directed by the A54 targeting peptide. Furthermore, the MRI diagnostic efficiency of A54-CaPNPs was systematically investigated in an orthotopic liver cancer model and primary HCC model. In vivo MRI experiments showed that A54-CaPNPs had higher sensitivity in the BEL-7402 orthotopic liver cancer model with a more remarkable contrast enhancement and a longer imaging time compared to those without A54 modification. Moreover, the experiments on primary HCC models suggested that A54-CaPNPs showed greatly enhanced MR imaging performance in comparison with Gd-DTPA. These results suggest that A54-CaPNPs possess great potential to enable the non-invasive early diagnosis of primary HCC for timely surgical resection.