The influence of UV-radiation on the molecular characteristics of low-density polyethylene in dependence of samples' thickness and the dose has been investigated by methods of viscosimetry, light scattering, turbidimetry and gelation measuring. It was established that the destruction and crosslinking processes of macromolecules proceed simultaneously with the irradiation. In a range of doses previous to gelation increase of mass-average molecular mass and degree of branching of macromolecules accompany the irradiation. The intensity of change of the molecular characteristics is lowered along with the increase of samples' thickness, as soon as the basic molecular transformations occur in a thin him layer of the samples' surface. For the same reason the gelation point dose decreases along with the decrease of samples' thickness and the destruction-to-crosslinking speeds ratio rises up to a constant value, but lowers with decrease of samples' thickness. It has been assumed that the degree of change of molecular characteristics is independent of samples' thickness and mechanisms of influence of UV- and gamma-irradiation on polyethylene is similar.