The atom-bond connectivity and the generalized atom-bond connectivity indices have shown to be useful in the QSPR/QSAR researches. In particular, the atom- bond connectivity index has been applied to study the stability of alkanes and the strain energy of cycloalkanes. In this paper we obtain some bounds on these indices in terms of graph parameters. To obtain these bounds we use the mathematical tools from analysis. Some of these bounds for ABCalpha improve, when alpha = 1/2, known results on the ABC index.