Cellulite is associated with a complex array of adipocytes under the skin and vascular system. A herbal compress that was previously developed was proven to have an anti-cellulite effect in healthy volunteers within 2 weeks of treatment. However, its mechanism and ingredients responsible for reducing cellulite were not known. The purpose of this study was to investigate the activity of eight essential oils in, and two water extracts from, the ingredients of the herbal compress together with nine monoterpenoid constituents on the 3T3-L1 adipocytes. The vasodilatory effect on rat aortae was also studied. The adipocytes were induced by dexamethasone, 3-isobutyl-1-methylxanthine and insulin. At all concentrations tested, all essential oils, water extracts and their monoterpenoid constituents significantly inhibited lipid accumulation activity (p < 0.05) and decreased the amount of triglycerides when compared to untreated cells (p < 0.01). In addition, our results showed that the mixed oil distilled from the herbal compress mixed ingredients could relax the isolated rat aorta (EC50 = 14.74 ± 2.65 µg/mL). In conclusion, all essential oils, extracts and chemical constituents tested showed effects on adipogenesis inhibition and lipolysis induction on the cultured adipocytes with the mixed oil demonstrating vasorelaxation activity, all of which might be the mechanisms of the anti-cellulite effects of the herbal compress.