Ethylene oxide (EO) – propylene oxide (PO) copolymers have been used as components of various functional materials. Detailed analyses of them, however, still remain challenging. As it turns out, it is difficult to detect all of the components by using mass spectrometry alone without chromatographic separation due to ion suppression effects. In this work we analyzed an EO-PO random copolymer by using an LC – MALDI-SpiralTOF MS system, with the expectation of detecting more components as a result of reduced ion suppression effects.