This thesis deals with a whisker sample made up of the high-temperature superconductor YBCO. The first aim is to investigate whether the paraconductivity behaviour for this material can be accounted for by means of the model proposed by A.I.Larkin and A.A.Varlamov in the framework of the Ginzburg-Landau theory. Concerning this issue, estimates for the microscopic parameters introduced by the model have also been obtained. The second aim is to study how the elecrical properties of the YBCO whisker modify when reducing its cross-section area by means of a Focused Ion Beam device, from about 77 micron^2 to about 4 micron^2, over a length of about 150 micron. In this respect, a deep analysis has been carried out for the geometrical and morphological effects induced by the FIB etching.