Human T cell leukemia virus 1 (HTLV-1) is a retrovirus belonging to the family of Retroviridae and causes adult T cell leukemia (ATL) and HTLV-1-associated myelopathy (HAM). HTLV-1 subtype C is highly prevalent in the indigenous peoples of central Australia with over 40% adults were testing seropositive in 20181. The viral capsid is essential for the maturation of virions and protects the RNA genome from hydrolysis by cytosolic enzymes. Here, we report novel structural information of HTLV-1 capsid protein (CA) by crystallising the N-terminal domain (NTD), C-terminal domain (CTD) and full-length, respectively. Intriguingly, three crystal forms with different space groups of NTD were obtained: 1) triclinic P 1 with an ultra-high resolution of 0.87 Å that offers unambiguous atomic information of each residue, including the N-terminus β-hairpin which is important in HIV-1 CA for nucleotides transport2; 2) hexagonal P 6 2 2 which diffracted to 2.05 Å showing that crystallographic six-fold symmetry appears in the hexagonal capsid lattice, indicating HTLV-1 CA could potentially assemble to a hexameric conformation that is canonical in HIV-1 CA hexamer; 3) orthorhombic P 212121 diffracted to 1.47 Å displaying that a sulfate occupies the positively charged pocket, enclosed by H71/72, R98 and W117, implying HTLV-1 CA might interplay with new cellular factors that are different from the cofactors interacting with the HIV-1 capsid. The HTLV-1 CA-CTD was also solved to 1.47 Å and reveals the dimerisation packing of the capsid lattice. The crystal of HTLV-1 CA-full-length diffracted to 2.25 Å belonging to the F 2 2 2 space group, which also contains a six-fold crystallographic symmetry to generate a hexameric lattice. With the insight these structures have given us, we can predict how the HTLV-1 CA protein self-assembles and begin exploring how to disrupt the capsid pharmaceutically.