Background: Previous studies have shown an increased risk of second primary malignancies (SPMs) among diffuse large B-cell lymphoma (DLBCL) survivors; however, this has not been comprehensively examined by race/ethnicity. We utilized a large population-based database to examine disparities in SPM risk by race/ethnicity. Methods: From 17 United States population-based Surveillance, Epidemiology and End Results (SEER) program cancer registry areas, we identified 57,262 ≥12-month first-primary DLBCL survivors diagnosed between 2000-2019. Standardized incidence ratios (SIRs) and accompanying 95% confidence intervals (CIs) quantified SPM risk by race/ethnicity (non-Hispanic White, Black, Asian/Pacific Islander [API] and Hispanic), compared with the general population. Results: Overall, we observed 4,719 SPMs after DLBCL representing a 1.2-fold significantly increased risk (95% Confidence Interval [CI] = 1.16-1.23) compared to the general population and an excess of 23 cases per 10,000 person-years. SIRs for all second cancers combined varied significantly by race/ethnicity with APIs and Hispanics presenting higher overall SPM risk [SIR_API: 1.42 (CI = 1.27-1.59), and SIR_Hispanic: 1.31 (CI = 1.19-1.43)] compared to the White or Black patients [SIR_white: 1.17 (CI = 1.13-1.21), SIR_Black: 1.16 (CI = 1.03-1.30)] (p-heterogeneity < 0.001). Heterogeneity by race/ethnicity in SIRs was even more pronounced in DLBCL survivors diagnosed at a younger age, those who were ≥5 years into their survivorship, those who had received chemotherapy, or those who had received no radiation as their initial treatment. Although SIRs for SPM was significantly higher for advanced stage DLBCL survivors (compared to those with a localized/regional disease), heterogeneity by race/ethnicity in SPM risk was significant regardless of the stage. Results from site specific analyses reported significantly higher overall SIRs for second hematological malignancies compared to solid cancers [SIR_hemat: 3.52 (CI = 3.22-3.85), and SIR_solid: 1.08 (CI = 1.04-1.11)]. Patterns by race/ethnicity also varied significantly by second cancer type, particularly for second primary anal cancer, Hodgkin’s lymphoma (HL), and Acute Non-Lymphocytic Leukemia (ANLL) (p < 0.001 for each). Strikingly elevated SPM risks (SIRs > 10) were observed for second primary anal cancer, HL and ANLL among the Black patients, and HL among the APIs and Hispanic DLBCL survivors, compared to the white patients. Conclusions: Using a large-scale population-based data, we observed substantial disparities in SPM risk by race/ethnicity, with patients belonging to minority groups experiencing higher risks. SPMs have emerged as an important challenge for DLBCL survivors, therefore, further research to understand drivers of the observed race/ethnicity heterogeneity is warranted.