We measure voltage-current curves at low temperature in La2/3B1/3MnO3 samples (B=Ca,Sr). The powder oxides were prepared by different wet-chemical routes and low calcination temperatures were used for nanoparticles formation. We studied samples prepared by three different synthesis methods: gel-combustion, urea sol-gel and liquid-mix. Although the average particle size was almost the same for all the samples (∼30 nm), we found different behaviors in the V-I curves depending on the synthesis route. The obtained data are analyzed in the electronic tunneling picture.