Abstract: The stability, magnetic and electronic properties of transition metal (TM) Fe or Cr monoatomic chain encapsulated into (6, 6) Cu nanotube (Fe@CuNT or Cr@CuNT) were systematically investigated by the first-principles calculations based on density-functional theory. The results indicate that the binding energies per TM atom of the Fe@CuNT and Cr@CuNT hybrid structures are remarkably higher than those of corresponding freestanding TM chains, indicating the TM chains are significantly stabilized by the Cu nanotube coating. The formed bonds between outer Cu and inner TM atoms show metallic bonding character. The magnetic ground states of Fe@CuNT and Cr@CuNT hybrid structures are ferromagnetic and antiferromagnetic states, respectively. The spin and orbital magnetic moments of inner Fe and Cr atoms of Fe@CuNT and Cr@CuNT hybrid structures were calculated. The magnetocrystalline anisotropy energies (MAE) of Fe@CuNT and Cr@CuNT hybrid structures are all significantly enhanced compared to those of corresponding freestanding TM chains, suggesting that Fe@CuNT and Cr@CuNT hybrid structures can be used in ultrahigh density magnetic storage. Furthermore, the easy magnetization direction switches from that along the chain direction in freestanding Fe chain to that perpendicular to the chain direction in Fe@CuNT hybrid structure. The large spin polarization at the Fermi level also makes the Fe@CuNT hybrid structure interesting as a potential candidate for spin-dependent transport applications.