Effects of the mixed additive containing tartaric acid and La3+ on the crystallization of calcium oxalate in silica gel were investigated by means of X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy and scanning electron microscopy(SEM).The results indicated that artaric acid could inhibit the growth and aggregation of the crystal,and induce the formation of calcium oxalate dehydrate(COD).La3+ could also induce the COD formation and affect the morphology of calcium oxalate monohydrate(COM).While the mixed additive of tartaric acid and La3+ could not only enhance the ability of inducing the COD formation,but also inhibit the COM aggregation and decrease the COM surface area.The mixed additive of tartaric acid and La3+ is worthy to be considered for the prevention and treatment of urolithiasis.