The effects of structural, electrical and magnetic properties with the isovalent chemical substitution of Ca2+ into the Sr2+ sites in new series of two-dimensional La1.2(Sr1.8-xCax)Mn2O7 compounds (x=0∼0.8) and three-dimensional La0.6(Sr0.4-xCax)MnO3 compounds (x=0∼0.4) are investigated. The Curie temperatures (TC) decreased from 135 K to 102 K and 370 K to 270 K for x = 0 to 0.4 in La1.2(Sr1.8-xCax)Mn2O7 and La0.6(Sr0.4-xCax)MnO3, respectively. The antiferromagnetic behavior with Néel temperature around 30 K was found in the x=0.8 sample in La1.2(Sr1.8-xCax)Mn2O7. The composition induced structural variation has been found in La0.6(Sr0.4-xCax)MnO3. All the results demonstrate that the dimensionality and chemical size play an important role in controlling the colossal magnetoresistance in manganites.