We have studied a weak charge-ordering behavior in phase separated (Ln1/3Sm2/3)2/3Ca1/3MnO3 (Ln=Pr and La) manganites with same hole doping but slightly different tolerance factors. The M (T) and ρ (T) curves of the Pr-sample showed an anomaly caused by a weak charge-order (CO) transition at ∼210 K, while that of La-sample did not. However, the La-sample displayed a weak anomaly related to the CO instability in the derivative curve of the temperature dependent magnetoresistance. This result is understood on the basis that the CO phase in La-sample is partly suppressed by a large magnetic field of ∼80 kOe, while in Pr-sample it is not collapsed in that field scale. Our data support the existence of charge-ordering, electronic phase separation and a field-induced reduction of weak CO instability for La-sample, which can contribute towards high MR especially at lower temperatures due to partial melting of CO phase and/or percolation behavior. © 2007 Elsevier Ltd. All rights reserved.