Abstract. Letẋ = f (x) be a C k autonomous differential system with k ∈ N ∪ {∞, ω} defined in an open subset Ω of R n . Assume that the systemẋ = f (x) is C r completely integrable, i.e. there exist n − 1 functionally independent first integrals of class C r with 2 ≤ r ≤ k. If the divergence of systemẋ = f (x) is non-identically zero, then any Jacobian multiplier is functionally independent of the n − 1 first integrals. Moreover the systemẋ = f (x) is C r−1 orbitally equivalent to the linear differential systemẏ = y in a full Lebesgue measure subset of Ω. For Darboux and polynomial integrable polynomial differential systems we characterize their type of Jacobian multipliers.