In this paper, we study the Lie symmetries and the conserved quantities of non-holonomic mechanical systems withunilateral Vacco constraints. We give the conditions and the form of conserved quantities due to the Lie symmetriesof the systems, and present the inverse problem of the above problem, i.e. finding the corresponding Lie symmetrytransformation according to a given integral of the system. Finally, we give an example to illustrate the application ofthe results.