Abstract Introduction In recent years there has been a surge of research on plurisexuality (the ability to experience attraction to more than one gender). Evidence strongly suggests that plurisexual people experience desire differently, face unique stressors, and have increased risk for sexual dysfunction compared to gay and lesbian groups (Björkenstam et al., 2020). These factors may differ between plurisexual people in same-gender relationships and those in mixed-gender relationships. Fantasy and desire, two fundamental constructs of sexology theory and sex therapy, merit further research in this population. Objective We hypothesize that plurisexual people experience fantasy and desire differently depending on their relationship type (same-gender vs. mixed-gender). Methods Data was collected for a larger study of sexual health and behaviors in undergraduate students at a large university in the Midwestern US. The sample included participants in relationships (n=493; mean age = 20.48 years; 80% women, 16% men, 4% gender minority; 78% White). Respondents who identified as “bisexual,” “pansexual,” “mostly heterosexual,” “mostly lesbian/gay,” or a combination of these were coded as plurisexual, and other respondents (e.g., “heterosexual,” “lesbian/gay,” “asexual”) were coded as not plurisexual. Respondents were coded as being in same-gender relationships if they identified as a man dating a man, a woman dating a woman, or any gender minority (e.g., “non-binary,” “gender fluid”) dating a man, woman, or other gender minority person (i.e., relationships likely to be perceived as queer). Respondents were coded as being in mixed-gender relationships if they identified as a man dating a woman or a woman dating a man. Fantasy was measured with an adapted Sex Fantasy Questionnaire (SFQ; Wilson, 1988), and desire with the Sexual Desire Inventory-2 (Spector, Carey, & Steinberg, 1996). We conducted two-way ANOVAs to evaluate the influence of plurisexual identity and relationship type on fantasy and desire. Results There was a significant main effect of plurisexual identity on sexual fantasy (F(1, 391)=58.61, p<0.01) and desire (F(1, 469)=7.26 p<0.01), with plurisexual participants reporting higher levels of both. There was also a significant interaction effect between plurisexual identity and relationship type for fantasy (F(1, 391)=4.73, p=0.03) and sexual desire (F(1, 469)=5.78, p=0.02), such that the effect of plurisexuality was amplified for participants in mixed-gender relationships and attenuated for participants in same-gender relationships (see Figures). Conclusions Results suggest that plurisexual people experience higher levels of fantasy and desire when in mixed-gender vs. same-gender relationships. These differences could be attributed to perceptions that plurisexual people in same-gender relationships are queer and those in mixed-gender relationships are straight (Arriaga & Parent, 2019). Additionally, the fluidity of sexual identity suggests that experiences of attraction, desire, and fantasy change substantially based on the gender of one’s partner (Diamond, 2008). Clinically, our findings point to different applications of interventions on fantasy intended to stimulate desire in plurisexual patients with low desire, address desire discrepancy between partners, or separate problematic desire from behavior. As most research surrounding fantasy and its role in desire was developed in straight cisgender samples, clinicians and researchers should consider sexual orientation, relationship type, and their interaction when intervening upon fantasy. Disclosure No.