Letp=(p1,p2,...) be a vector with an infinite number of coordinates, 1≦pk≦,k=1,2,... On the set of random functions depending on infinite number of variables, a mixed norm ∥.∥p is introduced, and thus the spacesLp with mixed norm are defined. Part 1 contains observations of general properties of those spaces (in particular, convergence properties depending on the behaviour of the exponentspk ask→ ∞). Part 2 contains the proof of infinite-dimensional version of S. L. Sobolev's theorem (in mixed norm) for potentials of Wiener semigroup on infinite dimensional torusT∞.