Using the method of threshold Frederick's transitions in magnetic field were determined the values of splay orientational elastic constants K-11 of the nematic trimers 4, 4'-bis-[omega-(4-cyanobiphenyl-4'-yloxy)alkyloxy]biphenyls with the number n of CH2 groups in their spacers from 3 to 10. The dramatic odd-even effect in the dependence of Kt I versus n for trimers was evaluated. This effect is mainly due to the oscillations of the degree of intermolecular orientational order in the series of the compounds under investigation. Using the values of K-11 the values of the dielectric anisotropy Delta epsilon of nematic trimers were calculated. The data obtained for trimers were compared with the same characteristics for dimers (4,4'-bis-cyanobiphenyloxyalkanes).