A Roman dominating function of a graph G is a function f : V (G) → {0, 1, 2} such that whenever f(v) = 0 there xists a vertex u adjacent to v such that f(u) = 2. The weight of f is w(f) = Pv∈V (G) f(v). The Roman domination number γR(G) of G is the minimum weight of a Roman dominating function of G. In this thesis, we give linear time algorithms for finding Roman domination numbers of interval graphs and strongly chordal graphs. We also give sharp upper bounds of Roman domination numbers for some classes of graphs.