A multi-core amplification optical fiber includes a plurality of core portions doped with a rare-earth element, and a cladding portion positioned at an outer periphery of each of the core portions and having refractive index lower than refractive index of each of the core portions, in which when a concentration of the rare-earth element doped to each of the core portions is 250 ppm to 2000 ppm, a relative refractive index Δ of each of the core portions relative to the cladding portion is 0.5% to 2% at a wavelength of 1550 nm, and a core diameter of each of the core portions is 1 µm to 5 µm, a separation distance between each of the core portions and adjacent one of the core portions is set at equal to or larger than 30 µm and at equal to or smaller than 60 µm so that a crosstalk of light between the adjacent core portions is equal to or lower than -30 dB. Hereby a multi-core amplification optical fiber and a multi-core optical fiber amplifier capable of optical amplification while suppressing lowering of the qualtity in signal light are provided.