Let \(\mathfrak {R}\) be a commutative ring with identity \(1\ne 0\) and \(Z(\mathfrak {R})\) denotes the set of zero-divisors of \(\mathfrak {R}\) . The zero-divisor graph of \(\mathfrak {R}\) , denoted by \(\Gamma (\mathfrak {R})\) , is a simple undirected graph having vertex set \(Z(\mathfrak {R})^*\) (set of nonzero zero-divisors of \(\mathfrak {R}\) ) and two distinct vertices a and b are joined by an edge if and only if \(ab=0\) . In this article, we find the signless Laplacian spectrum of the graph \(\Gamma (\mathbb {Z}_\mathfrak {n})\) , for \(\mathfrak {n}=\phi _1^{M} \phi _2\phi _3\) , when M is even and odd integer, and for \(\mathfrak {n}=\phi _1^{M_1} \phi _2^{M_2}\phi _3\) , where \(M_1, M_2\) are positive integers and \(\phi _1,\phi _2\) and \(\phi _3\) are primes \((\phi _1 < \phi _2<\phi _3)\) .