  Strained thin films of charge/orbital ordered (CO/OO) $Nd_{0.5}Ca_{0.5}MnO_3$
(NCMO) with various thickness have grown on (100)-SrTiO$_3$ and (100)-LaAlO$_3$
substrates, by using the Pulsed Laser Deposition (PLD) technique. The thickness
of the films influences drastically the transport properties. As the thickness
decreases, the CO transition increases while at the same time the
insulator-to-metal transition temperature decreases under application of a 7T
magnetic field. Clear relationships between the structural distortions and the
transport properties are established. They are explained on the basis of the
elongation and the compression of the Mn-O-Mn and Mn-O bond angles and
distances of the \QTR{it}{Pnma} structure, which modify the bandwidth and the
Jahn-Teller distortion in these materials
