The invention discloses a float glass plate and a method of manufacturing thereof. The present invention relates to a float glass plate that is formed by continuously supplying a molten glass onto a molten metal in a bath and allowing the molten glass to flow on the molten metal, wherein the float glass plate satisfies the following expression (1) (as shown in the description) when, on a coordinate axis that is parallel to a through-thickness direction and has, as an origin, an arbitrary point on a principal surface which is positioned on the molten metal side in the bath among both principalsurfaces of the float glass plate, a water concentration in glass at a coordinate x ([mu]m) indicating a distance from the origin is represented by C(x) (mass ppm), the thickness of the float glass plate is represented by D ([mu]m), a maximum value of the C(x) is represented by Ca (mass ppm), and a coordinate at which the C(x) is maximum is represented by Da ([mu]m).