Let X be a locally compact space, and L ∞ 0 (X, ι) be the space of all essentially bounded ι-measurable functions f on X vanishing at infinity. We introduce and study a locally convex topology β 1 (X, ι) on the Lebesgue space L 1 (X, ι) such that the strong dual of (L 1 (X, ι), β 1 (X, ι)) can be identified with (L ∞ 0 (X, ι), · ∞ ). Next, by showing that β 1 (X, ι) can be considered as a natural mixed topology, we deduce some of its basic properties. Finally, as an application, we prove that L 1 (G), the group algebra of a locally compact Hausdorff topological group G, equipped with the convolution multiplication is a complete semitopological algebra under the β 1 (G) topology.2010 Mathematics subject classification: primary 46A03, 46A70; secondary 46H05, 43A20.