Background: Health risks and outcomes among Asian American patients are not adequately understood when Asians are treated as a homogenous ethnic group. This work is the first to explore trends in time to surgical treatment for breast cancer amongst Asian American ethnic subgroups. Methods: We used data from the population-based California Cancer Registry to identify a cohort of females diagnosed with invasive breast cancer between 2012-2017 in California. Time to surgical treatment was defined as the time elapsed between definitive diagnosis of breast cancer and receipt of surgery. Covariates included individual patient sociodemographic, health history, and tumor characteristics. Multivariable logistic regression was used to determine the odds of receiving surgery within 30 and 90 days of breast cancer diagnosis and multivariable Cox proportional hazards regression was used to analyze the likelihood of shorter time to surgery. A Bonferroni corrected alpha level was used to account for multiple racial/ethnic group comparisons. Results: Of 106,441 breast cancer patients, 57% were non-Hispanic white (NHW), 21% were Hispanic, 14% were Asian (4% Filipino; 3% Chinese; 1% each of Asian Indian or Pakistani (AIP), Vietnamese, Japanese, and Korean; 3% other Asian), and 6% were non-Hispanic black (NHB). Compared to NHWs, Hispanics (OR = 0.86, 99.5% CI = 0.82-0.92) and NHBs (OR = 0.82, 99.5% CI = 0.76-0.90) were less likely to receive surgery within 30 days of breast cancer diagnosis, while Chinese (OR = 1.30, 99.5% CI = 1.17-1.45) and AIPs (OR = 1.24, 99.5% CI = 1.04-1.48) were more likely to receive surgery within 30 days. These trends persisted for Hispanic (OR = 0.87, 99.5% CI = 0.79-0.96), NHB (OR = 0.73, 99.5% CI = 0.63-0.85), and Chinese patients (OR = 1.33, 99.5% CI = 1.04-1.71) when analyzing the likelihood of receiving surgery within 90 days of diagnosis. Compared to NHWs, Hispanics (OR = 0.94, 99.5% CI = 0.92-0.97), NHBs (OR = 0.88, 99.5% CI = 0.85-0.91), and Vietnamese (OR = 0.90, 99.5% CI = 0.83-0.98) were less likely to experience shorter time to surgical treatment, while Chinese (OR = 1.15, 99.5% CI = 1.09-1.21) and AIPs (OR = 1.09, 99.5% CI = 1.01-1.18) were more likely to have shorter time to surgery. Conclusions: In this population-based study of the California Cancer Registry, trends in time to surgical treatment for breast cancer were not consistent for patients belonging to different Asian ethnic subgroups. While Chinese and AIP patients tended to receive surgery sooner than NHW patients, Vietnamese patients face a disparity in receiving timely surgical treatment relative to NHW patients. Further research is needed to fully understand and appropriately target disparities in breast cancer treatment for patients of different Asian American ethnic subgroups.