Mechanical properties of the spray-cast Al 6061 alloy with variation of Mg/Si addition were investigated. After spray-cast, hot extrusion was performed at $460^{circ}C$ then followed ageing treatment to the T6 condition. SEM, EDX, and XRD were used to characterize a ${eta}(Mg_{2}Si)$ precipitate. The amount of ${eta}$ precipitate was calculated from the XRD measurements. Hardness, ultimate tensile strength and elongation were tested then compared with those of the Al 6061 alloys made by ingot metallurgy (I/M) and powder metallurgy (P/M). The ultimate tensile strength and elongation of the spray-cast Al 6061 alloy were 318MPa and 16.5%, respectively. These properties were improved in the 2.2 wt%Mg and 1.3wt%Si addition up to 349MPa of UTS and 12.5% of elongation, mainly due to increased amount of a fine supersaturated ${eta}(Mg_{2}Si)$ precipitate.