Higher-order nonlinear and dispersive effects on ion-acoustic solitons in a plasma consisting of two types of cold positive ions and two-temperature non-isothermal electrons are studied using a reductive perturbation method. An integrated form of the basic sets of fluid equations consisting of two types of positive ions and two types of non-isothermal electrons is derived in terms of a pseudo-potential. A perturbation solution of this equation is obtained by the Bogoliubov–Mitropolsky method. At the lowest order, we obtain a modified Korteweg–de Vries solitary-wave solution, which has a sech4 profile. Calculations are carried out at the next two higher orders. The secularity-removing condition at each order gives a correction to the velocity of the solitary wave at the corresponding order. The variations of Mach number and width of the ion-acoustic soliton with amplitude at each order are shown graphically for plasmas with H+ and He+ or with He+ and Ar+ ions, with two-temperature non-isothermal electrons.