Ferritin is an important protein for iron storage in cells. A hepatopancreas cDNA library from the mud crab Scylla paramamosain was constructed using the SMART technique. A complete cDNA sequence that showed high identity with the conserved sequence of the ferritin gene was cloned from the cDNA library and subjected to further investigation. The full-length ferritin gene of Scylla paramamosain (SpFer) consists of 767 bp and contains a complete open reading frame of 513 bp and a 26-bp iron-respective element in the 5′-untranslated region. The gene encodes a polypeptide of 170 amino acids, constituting a predicted molecular weight of 19.44 kDa and a theoretical isoelectric point of 5.24. The deduced protein shares 84% identity with the ferritin protein of the crab Eriocheir sinensis. Quantitative real-time PCR analyses revealed that the expression of ferritin was ubiquitous in different organs of S. paramamosain, including muscle, heart, ovary, testis, and hepatopancreas. The highest expression level was found in the heart, while testis tissue showed the lowest level. Ferritin mRNA expression in continuous developmental stages in zoeal phases, including Z1, Z2, Z3, Z4, and Z5, as well as megalopa and juvenile crab I stages, were also examined by quantitative real-time PCR. The expression level of ferritin was highest in the Z1 stage and lowest in the megalopa stage. This study provides useful information regarding the structure and function of ferritin and will play an important role in immunity and resistance research in S. paramamosain.