In this paper we show a regularity theorem for quasi-minima of scalar integral functionals of the Calculus of Variations with nonstandard growth conditions. Let us consider functionals as the following form F [u, Ω] = Ω f (x, u (x) , ∇u (x)) dx where f : Ω × R × R N → R is a Carathéodory function satisfying the inequalities |z| p − c 1 ≤ f (x, s, z) ≤ c 2 |z| βp * + |s| βp * + 1 for each z ∈ R N , s ∈ R and for L N-a. e. x ∈ Ω, where c 1 and c 2 are two positive real constants, with c 1 < c 2 , Ω is an open subset of R N , N ≥ 2, 1 < p < N and p p * < β <β p,N ≤ 1 where p * = N p N −p is the Sobolev conjugate of p andβ p,N is a positive real number.