Dielectric constants and losses have been measured for 1‐hexene, 1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene, 1‐pentadecene, 1‐hexadecene, 1‐heptadecene, and 1‐octadecene as pure liquids at up to 10 frequencies between 1 and 140 GHz at 25°C. The mean relaxation times,&tgr;0, and viscosities, &eegr;, increase significantly with increasing chain length; however, the parameter&tgr;0/&eegr;reaches a maximum for 1‐dodecene and then decreases with increasing chain length. The results are compared with those obtained for other n‐alkyl compounds containing a polar end group.