The first composition observation of energetic neutral atom (ENA) emissions during the main phase of a geomagnetic storm is reported here. The measurements were made by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail on October 22, 1999 when the ring current was strengthening. For this geomagnetic storm, while the Dst index was monotonically decreasing during the main phase, ENA fluxes showed two major enhancements with distinctly different temporal profiles. For the first enhancement, the increases in ENA fluxes were rapid and the subsequent evolution was species dependent. Both the integral ENA (E>~12 keV) and neutral hydrogen (E>67 keV) fluxes remained relatively unchanged after the increase while the neutral oxygen (E>203 keV) fluxes decreased rapidly. For the second enhancement, the increases in ENA fluxes of all species were rather gradual and the subsequent decrease in the neutral oxygen flux was also slow. The slow decrease may be related to the continual AE enhancement during that time. For total energies above 200 keV, the intensity of ENA oxygen was the highest, followed by hydrogen, and then by helium. This ordering of ENA intensity for these species is similar to the previous ENA composition results obtained for the recovery phase of another geomagnetic storm. ¿ 2001 American Geophysical Union