Let Ω ⊂ R N , N ≥ 2, be an open bounded connected set. We consider the fractional weighted eigenvalue problem (−∆) s u = λρu in Ω with homogeneous Dirichlet boundary condition, where (−∆) s , s ∈ (0, 1), is the fractional Laplacian operator, λ ∈ R and ρ ∈ L ∞ (Ω). We study weak* continuity, convexity and Gâteaux differentiability of the map ρ → 1/λ 1 (ρ), where λ 1 (ρ) is the first positive eigenvalue. Moreover, denoting by G(ρ 0 ) the class of rearrangements of ρ 0 , we prove the existence of a minimizer of λ 1 (ρ) when ρ varies on G(ρ 0 ). Finally, we show that, if Ω is Steiner symmetric, then every minimizer shares the same symmetry.Recently, great attention has been focused on the study of fractional and nonlocal operators of elliptic type, both for pure mathematical research and in view of concrete real-world applications. This type of operators arises in a quite natural way in many different contexts, such as, among others, the thin obstacle problem,