In engineering applications, many reliability systems can be modeled as k-out-of-n systems with components having random weights. Before putting such kind of system into a working state, it is of great significance for a system designer to find out the optimal assembly of the random weights to the components. In this article, we investigate the performance levels of k-out-of-n systems with random weights. Optimal assembly policies are obtained by maximizing the total capacity according to different criteria, including the usual stochastic order, the increasing convex [concave] order, and the expectation order. Based on the optimal assembly strategy derived by maximizing the expected total capacity, we further investigate stochastic properties of the resulting weighted system with respect to the vector of expectations of random weights. Numerical examples are provided to highlight our theoretical findings as well. KEYWORDS expected total capacity, LWSAI, optimal assembly, random weighted k-out-of-n system, RWSAI, SAI, stochastic orders, total capacity 1 Hereafter, for convenience, we denote the k-out-of-n system with random weights by r-w-k-out-of-n system. Formally, the definition of a r-w-k-out-of-n system is recalled as follows. Let X = (X 1 , … , X n ) be the component lifetimes vector, and W = (W 1 , … , W n ) be the random weights vector with W i denoting the weight of the ith component. Let (t; k, Naval Res Logistics 2018;65:347-359 wileyonlinelibrary.com/journal/nav