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The influence of substitution Pr for La and Ni for Co on hydrogen storage properties of Pr1-xLaxMgNi4-yCoy (х = 0; 0.5, у = 0–3) alloys were studied. The existences of solid solutions have been found. It is shown that the synthesized alloys absorb hydrogen at room temperature and hydrogen pressure 0.1–10 bar. For some of the studied compounds, the formation of hydrides with cubic and orthorhombic structures was found. Hydrogen capacity for Pr1-xLaxMgNi4-yCoy alloys increases with Co content increasing and reaches 6.6 H/f.u. for PrMgNi2Co2. For electrochemical hydrogenation different trend was observed. With increasing of Co content discharge capacity slightly increases only to y = 0.5, and after y > 0.5, decreases. Highest discharge capacity is equal to 305 mА∙h/g for Pr0.5La0.5MgNi3.5Co0.5, and 268 mА∙h/g for PrMgNi3.5Co0.5 at current densities 50 mА/g and 200 mA/g, respectively. Influence of Co and number of activation cycles on HRD value of PrMgNi4-yCoy alloys was investigated. Additionally, obtained results of the electrochemical properties were compared with related compounds.