The properties of oblique propagation of small amplitude ion-acoustic soliton are investigated in a
plasma containing weakly relativistic ions and two-temperature electrons (cold and hot electrons). The
reductive perturbation method is used to derive the Korteweg−de Vries equation for the present plasma
model. It is found that the parameters determining the nature of soliton are different for compressive or rarefactive structures. Moreover, the effects of weakly relativistic ions, the temperature ratio, and the
density ratio of hot-to-cold electron species on soliton characters are studied. The theory is applied on the
case of relativistic ions observed in the magnetosphere and in the case of nonrelativistic ions observed in tokamaks.