Magnetic refrigeration is an environmentally friendly cooling technology, which is believed to be significantly more efficient than the currently employed gas-compression-based cooling technologies. The commercialization of this technology is crucially dependent on the discovery of materials that exhibit large magnetocaloric effects and can be easily fabricated using cheap, non-toxic, and readily available elements. The intermetallic Mn_1-xFe_x-δNi_δSi_1-yAl_y compounds are known to exhibit large magnetocaloric effects at the relatively low magnetic field (H = 2T or lower) and tunable phase transition 1, 2. These materials have gained much interest in recent years due to the fact that the constituent elements are cheap and readily available. However, selected drawbacks including large thermal hysteresis and mechanical instability make these materials unsuitable for application. More research efforts are required to eliminate these drawbacks so that the application potential for these materials can be realized. Therefore, we have synthesized the substitution of Ni with Co in Mn_0.5Fe_0.5Ni_1-xCo_xSi_0.94Al_0.06 (0.025 ≤ x ≤ 0.075) alloys by arc melting followed by a rapidly quenched vacuum suction casting technique and study the magnetic and magnetocaloric properties of the system, which has not been reported yet. X-ray diffraction and scanning electron microscopy (SEM) data indicated that the samples exhibited a single-phase. Peak magnetic entropy changes of (– ΔS_M) of as-cast alloy with x =0.025 is found to be 12 and 31 J kg-1K-1 for ΔH = 2 and 5 T, respectively around 225 K. The observed large MCEs are due to the first order magneto-structural phase transition exhibited by the materials from low-temperature ferromagnetic orthorhombic phase to high-temperature paramagnetic hexagonal phase. In this presentation, we present details of phase purity, microstructure, and magnetic properties of as-prepared and heat-treated alloys with 0.025 ≤ x ≤ 0.075