In this paper, we discuss the existence of at least three weak solutions for the following impulsive nonlinear fractional boundary value problem \begin{align*} {}_t D_T^{lpha} eft({}_0^c D_t^{lpha}u(t)\right) +a(t)u(t)&= ambda f(t,u(t)), \quad teq t_j, ext{a.e. } t ı [0, T], \Deltaeft({}_t D_T^{lpha-1} eft({}_0^c D_t^{lpha}u\right)\right)(t_j)&= I_j(u(t_j)),\quad j=1,... n, u(0) = u(T) &= 0 \end{align*} where $\alpha \in (\frac{1}{2}, 1]$, $a \in C([0, T ])$ and $f : [0, T ]\times\mathbb{R}\to\mathbb{R}$ is an $L^1$-Carathéodory function. Our technical approach is based on variational methods. An example is provided to illustrate the applicability of our results.