This paper deals with existence, uniqueness and global behaviour of a positive solution for the fractional boundary value problem Dβ(ψ(x)Φp(Dαu))=a(x)uσ in (0,1) with the condition x→0limDβ−1(ψ(x)Φp(Dαu(x)))=x→1limψ(x)Φp(Dαu(x))=0andx→0limDα−1u(x)=u(1)=0, where β,α∈(1,2] , Φp(t)=t∣t∣p−2 , p>1, σ∈(1−p,p−1) , the differential operator is taken in the Riemann–Liouville sense and ψ,a:(0,1)⟶R are non-negative and continuous functions that may are singular at x=0 or x=1 and satisfies some appropriate conditions