-Critical phenomena can show unusual phase diagrams when defined in complex network topologies. The case of classical phase transitions such as the classical Ising model and the percolation transition has been studied extensively in the last decade. Here we show that the phase diagram of the Bose-Hubbard model, an exclusively quantum mechanical phase transition, also changes significantly when defined on random scale-free networks. We present a mean-field calculation of the model in annealed networks and we show that when the second moment of the average degree diverges the Mott-insulator phase disappears in the thermodynamic limit. Moreover we study the model on quenched networks and we show that the Mott-insulator phase disappears in the thermodynamic limit as long as the maximal eigenvalue of the adjacency matrix diverges. Finally we study the phase diagram of the model on Apollonian scale-free networks that can be embedded in 2 dimensions showing the extension of the results also to this case.Introduction. -Recently great attention [1, 2] has been addressed to critical phenomena unfolding on complex networks. In this context it has been observed that the topology of the networks might significantly change the phase diagram of dynamical processes. For example when networks have a scale-free degree distribution P (k) ∼ k −λ and the second moment k 2 diverges with the network size, i.e. λ ∈ (2, 3] the Ising model [3][4][5][6], the percolation phase transition [7,8] and the epidemic spreading dynamics on annealed networks [9] are strongly affected. Moreover the spectral properties of the networks drive the epidemic spreading on quenched networks [10,11], the synchronization stability [12,13], the critical behavior of O(N ) models [14,15] and the critical fluctuations of an Ising model on spatial scale-free networks [16]. Quantum critical phenomena also might depend on the topology of the underlying lattice as it has been shown for Bose-Einstein condensation in heterogeneous networks [17]. Although large attention has been devoted to classical critical phenomena on scale-free networks, the behavior of quantum critical phenomena on scale-free networks has just started to be investigated.In particular the Anderson localization [18,19] was studied in complex networks showing that by modulating the clustering coefficient of the