We report pulse ESR studies of the electron spin relaxation processes in graphene. The linear temperature dependences of relaxation rates corresponding to T-1 approximate to T-2 similar to 0.1-1 mu s, similar values of g-factors of possible paramagnetic centres, and the Lorentzian lineshape of the signal indicate the bottleneck effect in spin relaxation of the strongly coupled homogeneous spin system of localized spins and conduction electrons. Interpretation of the data in the frames of the theory of strongly interacting localized and delocalized magnetic moments gives the spin relaxation time of the conduction electrons of an order of 5-30 ns, depending on the paramagnetic centres concentration. (C) 2012 Elsevier B.V. All rights reserved.