Polystyrene compositions with the high-T(c) superconductor (HTSC) YBa2Cu3O7-delta were prepared and a study of their diamagnetic responses was carried out at the frequency f = 50 kHz, depending on HTSC content (c = 0-100 vol.% with 5% steps) and temperature (T = 77-300 K). The results presented allow us to conclude that the diamagnetic behaviour of composites is of percolation character, and the critical volume fraction of HTSC is in the region of 0.20 < c < 0.30. The increase of the diamagnetic response in composites with increasing c is the result of formation and merging of a winding superconductive labyrinth consisting of YBa2Cu3O7-delta grains. The electrical resistance rho of composites shows a sharp decrease from 10(14) to 10(4) OMEGA cm, which depends on c in the region of 0. 20 < c < 0. 30.