BiScO3-PbTiO3 (BSPT) thin films with the thickness from 80 to 800 nm were fabricated via a sol-gel method on Pt(111)/Ti/SiO2/Si(001) substrates, and the effects of thickness on the structure and properties of the sol-gel-derived BSPT thin films were investigated. All the films with different thickness showed similar random orientation and similar grain size. The dependence of dielectric and ferroelectric properties on film thickness and temperature from room temperature to -190 degrees C were investigated, and the results were explained by comparing our experiment data with the existing experimental and theoretical models. It is found that the interface between the electrode and the film has a twofold deleterious effect on permittivity: firstly, a passive layer exists, secondly this layer pins domain walls, and thus the larger dielectric response in thicker films and at higher temperatures come from the higher mobility of domain wall motion. Piezoelectric properties dependence of the BSPT films on thickness were also investigated, the effective piezoelectric constant d(33)* increased from 35 pm/V for the film of 80-nm-thick to 80 pm/V of 800-nm-thick film.