Polycrystalline layered perovskite manganites Sm2-2xSr1+2xMn2O7 (x = 0.2, 0.4, 0.5) were synthesized by the citrate-gel method. Their magnetic and electric properties were investigated. The samples with x = 0.4 and 0.5 show insulating behavior. However, a metal-insulator (M-I) transition is observed for x = 0.2. The maximum value of MR [rho(0) - p(H)]/rho(0) x 100%] for x = 0.2 is 89.88% (105 K, 5 T) and 66.36% (105 K, 2 T). The MR is efficiently decreased from 57.62% (105 K, 5T) for x = 0.4 to 33.44% (105 K, 5T) for x = 0.5. Moreover, the Curie temperature (T-c) decreases with increasing x. (c) 2007 Elsevier B.V. All rights reserved.