This paper discusses the preparation of the colossal magnetoresistance samples L a0.7Sr0.3CrxMn1-xO3 (x=0, 0.10, 0.15) and La0.7Sr0.3FexMn1-xO 3 (x=0.05,0.10,0.16) by the sol-gel technique. The effects that the s ubstitution of Cr or Fe for Mn in La0.7Sr0.3MnO3 affects its structure, magnetic properties and magnetoresistance are also stud ied. Two peaks are observed on the resistance-temperature curves (R-T curves) of the two samples La0.7Sr0.3Cr0.15Mn0.85O3 and La0.7Sr0.3Fe0.05Mn0.9 5O3. The mechanism for the potential appearance of the double p eaks is discussed. A conclusion is drawn that with the increase of Cr (or Fe) s ubstituting for Mn, the samples' Curie temperature (TC), ferromagnetism and conductivity decrease， whereas their magnetoresistance strengthens. However, t he same amount of Cr produces less effect on the samples than the same amount of Fe.