Formation and fragmentation of beryllium clusters up to 100 atoms were studied using molecular dynamics trajectory simulations. Association rate constants of a single Be atom attachment to Ben clusters, n = 2-20, 30, 40, 50, 60, 70, 80, 90 and 100, and dissociation rate constants of these clusters were calculated directly. Dependence of the dissociation rate constants on temperature is strong and follows the Arrhenius equation. An analysis of the dissociation reactions has shown that beryllium clusters dissociate mainly into single Be atoms. The monomer association reaction depends weakly on temperature but strongly on the size of the cluster.