The inertness of polyethylene restricts its compatibility with other materials, Thus, the adhesion between polyethylene and various substrates usually requires surface pretreatments on the polyolefin in order to obtain satisfactory results. One different approach is the production of ethylene copolymers with small amounts of polar comonomers that can act as adhesion promoters. Using metallocene based catalysts, ethylene copolymers with 10-undecenoic acid (UA) and with 5,7-dimethylocta-1,6-diene (5,7DMO) were synthesised. The adhesion strengths of the copolymers in direct tension were measured. The obtained results show that UA/ethylene and 5,7DMO/ethylene copolymers exhibit higher adhesion strengths with increasing comonomer contents, UA/ethylene copolymers are more effective in improving adhesion properties than 5,7DMO/ethylene copolymers. This difference is easily understandable on the basis of the polarities of both comonomers.