We compute spectra of large stochastic matrices W , defined on sparse random graphs, where edges (i, j) of the graph are given positive random weights Wij > 0 in such a fashion that column sums are normalized to one. We compute spectra of such matrices both in the thermodynamic limit, and for single large instances. The structure of the graphs and the distribution of the non-zero edge weights Wij are largely arbitrary, as long as the mean vertex degree remains finite in the thermodynamic limit and the Wij satisfy a detailed balance condition. Knowing the spectra of stochastic matrices is tantamount to knowing the complete spectrum of relaxation times of stochastic processes described by them, so our results should have many interesting applications for the description of relaxation in complex systems. Our approach allows to disentangle contributions to the spectral density related to extended and localized states, respectively, allowing to differentiate between time-scales associated with transport processes and those associated with the dynamics of local rearrangements. There are numerous processes, both natural and artificial, which can be understood in terms of random walks on complex networks [1][2][3], including the spread of diseases in social networks [4,5], the transmission of information in communication networks (e.g.[6]), search algorithms [7,8], the out-of-equilibrium dynamics of glassy systems at low temperatures as described in terms of hopping between long-lived states in state space [9][10][11], the dynamics of major conformational changes in macro-molecules [12], or cell-signalling through protein-protein interaction networks [13], to name but a few. For reviews that cover several of these topics, see e.g. [14][15][16].The purpose of the present letter is to use random matrix theory to contribute to the understanding of systems of this type. We compute spectra of transition matrices for discrete Markov chains describing stochastic dynamics in complex systems. We construct these in terms of sparse random graphs in such a way that an edge (i, j) in a graph corresponds to a possible transition j → i, with the edge weight W ij > 0 quantifying the associated transitions probability, requiring i W ij = 1 for all j. We are interested in the limit, where the number N of possible states becomes large, with the average number of possible transitions at each state remaining finite in the thermodynamic limit (N → ∞).Given a time-dependent probability vector p(t) = (p i (t)), we have an evolution equation of the formThe condition W ij ≥ 0 for all (i, j) and the column sum constraint together entail that the spectrum of W is contained in the unit disc of the complex plane, σ(W ) ⊆ {z; |z| ≤ 1}. If W satisfies a detailed balance condition with an equilibrium distribution, p i = p eq i , such that W ij p j = W ji p i for all pairs (i, j), then W can be symmetrized by a similarity transformation -Our main interest here is the relation between eigenvalues of W and relaxation times of the Markov chain it describes...