The knowledge of the chemical distribution towards the Galactic anticentre is a powerful method for understanding the history of formation and evolution of the Milky Way. In this contribution it is described the self-consistent study of the physical and chemical properties of a sample of 23 HII regions observed in the optical range and located in a range of Galactocentric distances from 11 kpc to 18 kpc. Chemical abundances were derived for all the regions and their distribution along the Galactocentric distances were fitted to obtain the radial gradients of O/H, N/H, N/O, S/H, Ar/H, and He/H across the outermost part of the MW. The distribution of elements heavier than helium shows a clear decrease with distance. Although a shallower slope at large Galactocentric distances is suggested by our data, it does not necessarily imply a flattening of the gradient in the outer disc, but clearly shows that a linear extrapolation of the inner slope is inconsistent with the observations.