Understanding and control of ELMs are crucial issues for the operation of ITER where the Type-I ELMy H-mode has been chosen as the standard operation scenario. Determine whether ELM dynamic is chaotic or random is crucial to correctly describe the ELM cycle. In this paper, the dynamic characteristics of 8 ELM time-series from the JET tokamak are investigated. Characteristic parameters, such as the Hurst exponent and the Maximal Lyapunov Exponent, have been evaluated. The obtained results suggest the presence of deterministic chaos in some of the analysed time series.