Electro-optical properties of nematics of the trimer series (bis-(4-cyanobiphenyloxyalkaneoxy)-4,4’-biphenyls) have been investigated by the method of orientational elastic deformations in electric fields. The number n of CH2 groups in the oxyalkyl fragment was varied from n=2 to n=10. A strong odd-even effect was observed in the optical anisotropy Delta n and in the values of the threshold potential V-0 for the trimer nematics. These effects are respectively caused by oscillations in the degree of inter-and intramolecular orientational order when n is varied. The great difference in dependencies of Delta n and V-0 on n is discussed and compared with dimers data.