The spin splitting in zero magnetic field between the up- and down-spin electrons in a two-dimensional electron gas is obtained for a pseudomorphic InGaAs/In0.52Al0.48As graded heterostructure.We have studied the spin splitting in the heterostructure by means of the Shubnikov-de Haas oscillations.By analyzing the characteristic beating pattern of the oscillations,a spin splitting of 8.76meV was determined as B→0.