The effect of density and general distribution function on electrostatic ion-cyclotron waves is studied. The expression for the distribution function and growth rate of EIC waves is derived with multi-ion plasma (H+, He+ and O+) using particle aspect analysis. The plasma is considered to consist of resonant and non-resonant particles. The resonant particles participate in energy exchange while the non-resonant particles support the oscillatory motion of the wave. The wave is assumed to propagate obliquely to the static magnetic field. The effect of general loss-cone distribution function with varying plasma density is to enhance the growth rate of EIC waves with multi- component plasma (H+, He+ and O+). The loss-cone distribution acts as source of free energy. The results are interpreted for the space plasma parameters appropriate to the plasma sheet boundary layer region around the earth’s magnetosphere. The study may explain the EIC waves observed in this region and play a major role of particle density variation in particular region.