Fatty acids (FAs) have emerged as significant contributors to tumorigenesis, yet prospective evidence regarding their specific effects on lung cancer risk remains scarce. To investigate the association between plasma FAs and lung cancer incidence, as well as a potential modification effect of genetic susceptibility on lung cancer risk. A cohort study was conducted involving 112,547 cancer-free participants from the UK Biobank, with measurements of plasma FAs, including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) at baseline (2006-2010). Cox regression models were employed to assess lung cancer risk according to plasma FA quartiles or 1-SD increment. Furthermore, interaction between plasma FAs and polygenic risk score (PRS) was evaluated using an additive model. Over an average 10.9-year follow-up, 1122 lung cancer cases occurred. After multivariable adjustment, MUFAs were positively associated with lung cancer risk (hazard ratio [HR] per 1-SD = 1.32, 95% confidence interval [CI]: 1.13-1.54). In contrast, PUFAs, particularly n-3 PUFAs, n-6 PUFAs, docosahexaenoic acid, and linoleic acid, were associated with a lower risk of lung cancer, with HRs ranging from 0.79 (95% CI: 0.72-0.87) to 0.89 (95% CI: 0.83-0.95). SFAs were not significantly associated with lung cancer risk. Moreover, we observed an additive interaction between plasma PUFAs and genetic risk. Individuals with a high genetic risk and the lowest quartile of plasma PUFAs had the highest risk of lung cancer (HR = 2.20, 95% CI: 1.43-3.38). Our findings suggest that plasma PUFAs may serve as protective factors, while MUFAs represent risk factors for lung cancer, offering novel insights into lung cancer carcinogenesis and prevention.