Δ⁹-Tetrahydrocannabinol (Δ⁹-THC), an active ingredient of marijuana, evokes a number of biological effects including anti-cancer and anti-estrogenic actions. We and others have so far focused on and investigated the latter action. We recently reported that Δ⁹-THC up-regulates the expression of estrogen receptor β (ERβ, ESR2), resulting in the abrogation of 17β-estradiol (E2)-mediated ERα signaling (Takeda et al., Chem. Res. Toxicol., 26, 1073-1079, 2013). This finding may shed light on the possible endocrine-disrupting mechanism(s) employed by cannabinoids including Δ⁹-THC. Although previous studies have suggested that HU-210, a synthetic analog of Δ⁹-THC, evokes a set of endocrine alterations closely related to those of Δ⁹-THC, none have examined the effects of cannabinoids with a focus on the expression of ERβ, a “suppressive” molecule for ERα-mediated signaling. Thus, we herein determined whether HU-210 is also an endocrine modifier similar to Δ⁹-THC using ERα-positive MCF-7 cells in which the expression of ERβ is maintained at very low levels. The results of the present study revealed that HU-210, despite having a similar structure to Δ⁹-THC, did not modulate E2/ERα signaling or induce ERβ.