Integrated process for the production of bio-oil from sludge coming from a wastewater purification plant comprising the following steps: (a) sending wastewater to said purification plant obtaining sludge; (b) subjecting the sludge obtained in said step (a) to liquefaction, obtaining a mixture Including an oily phase consisting of bio-oil, a solid phase and an aqueous phase; (c) sending the aqueous phase obtained in said step (b) to said purification plant. The bio-oil (or “bio-crude”) thus obtained can be advantageously used in the production of bio-fuels which can be used as such, or in a mixture with other automotive fuels. Otherwise, said bio-oil (or “bio-crude”) can be used as such (bio-fuel), or in a mixture with fossil fuels (combustible oil, coal, etc.), for the generation of electric energy or heat.