Energy dispersive x-ray spectroscopy ofK&agr;transitions of neon and chlorine ions inside an electron cyclotron resonance (ECR) plasma is used to analyze the ion charge state distribution (CSD) inside the plasma. Basing on a computer code describing time dependent and stationary solutions of the balance equations for the CSD in ECR plasmas (considering single and multiple ionization and charge exchange processes, radiative recombination, vacancy cascades, and electron shake-off) and considering atomic properties (fluorescence yields, transition rates, x-ray energy shifts, x-ray production cross sections) of ions with different charge states, an approximation of simulated x-ray spectra to measured ones is possible. Thus the result we get is the corresponding CSD and information about the electron energy distribution function in the low energy region in the plasma. ©1998 American Institute of Physics.