We have characterized magnetization, transport, and structure of La2/3Ca1/3MnO3 thin films and bulk powder samples undoped and with low doping of 57Fe (1% and 3%) and Cr (6%, 7%, and 8%). The powder samples were synthesized by solid‐state reaction and thin films grown on (100)‐SrTiO3 STO, and (100)‐LaAlO3 LAO single‐crystal substrates by high O2 pressure (500 mTorr) using dc magnetron sputtering. We found changes in the values of the magnetoresistance and metal‐insulator transition temperatures, as well as the magnetization and Curie temperatures. These behaviors are dependent of the composition of the samples. However, we observed from the hysteresis loops that the coercitive field did not change significantly with Cr or Fe addition at different temperatures. Doping decreased the double exchange and the ferromagnetic order, possibly due to the competing influences from the strain relaxation.