Cosmological String Solutions by Dimensional Reduction

We obtain cosmological four dimensional solutions of the low energy effective string theory by reducing a five dimensional black hole, and black hole--de Sitter solution of the Einstein gravity down to four dimensions. The appearance of a cosmological constant in the five dimensional Einstein--Hilbert action produces a special dilaton potential in the four dimensional effective string action. Cosmological scenarios implemented by our solutions are discussed. (Talk presented at: ``27th Symposium on the Theory of Elementary Particles'' Wendisch--Rietz, September 7--11, 1993)