Objective To analyze the efficacy of breast-conserving surgery with adjuvant radiation therapy (BCS+RT) vs. mastectomy (MAST) for early breast cancer among young Chinese patients. Methods Young female breast cancer patients (≤40 years old) treated at West China Hospital of Sichuan University between January 1st, 2008, and December 31st, 2019 were analyzed for clinical staging, molecular subtypes, surgical techniques, and prognostic assessments using follow-up data. Results Of 974 eligible patients in this study, 211 underwent BCS+RT and 763 underwent MAST. The Kaplan-Meier analyses indicated that there was no significant difference in the 5-year locoregional recurrence-free survival rate (99.1% vs. 99.4%, P=0.299), distant metastasis-free survival rate (97.9% vs. 96.4%, P=0.309), breast cancer-specific survival rate (100.0% vs. 97.0%, P=0.209), or overall survival rate (99.4% vs. 96.8%, P=0.342) between patients who underwent BCS+RT and those who underwent MAST. The multiple Cox proportional hazards regression analyses revealed that the treatment approach (BCS+RT or MAST) did not significantly predict locoregional recurrence-free survival (P=0.427), distant metastasis-free survival (P=0.154), breast cancer-specific survival (P=0.155), or overall survival (P=0.263). Subgroup analyses showed that there was no statistically significant difference in survival outcomes between BCS+RT and MAST in different clinical stages or molecular subtypes. Clinical stage and molecular subtype should also not be regarded as independent factors in deciding the treatment approach. Conclusions Receiving BCS+RT or MAST treatment does not affect the survival outcomes of young early-stage breast cancer patients, showing similar efficacy across various clinical stages and molecular subtypes. Choosing BCS+RT is considered safe for early-stage young female breast cancer patients eligible for breast conservation.