Analysis of linear and cyclic polyamide-6 (PA-6) oligomer mixtures is an often needed task, that requires expensive equipment and/or chemicals or involved chemical procedures. We present an analytical method using electrospray ionization-mass spectrometry (ESI-MS) that has none of the mentioned difficulties. Measurements were performed on simple acidic aqueous solutions of oligomers. The method allowed qualitative and quantitative characterization of cyclic and Linear oligomers up to octamer. Scanning for both the positive, as well as negative ion fragments was used. Signal vs, concentration responses were determined for a number of lower oligomers. The method has the advantage of short analysis times and the use of relatively accessible instrumentation.