Purpose: To investigate the predictors of contralateral hypertrophy in patients treated with unilobar transarterial radioembolization (TARE) with yttrium-90-loaded resin microspheres due to unresectable right-liver tumors. Methods: Patients who underwent right unilobar TARE with resin microspheres between May 2019 and September 2021 were screened retrospectively. Contralateral hypertrophy was evaluated by calculating the kinetic growth rate (KGR) in 8–10 weeks after TARE. The predictors of increased KGR were determined with linear regression analysis. Results: A total of 24 patients (16 with primary and 8 with metastatic liver tumors) were included in the study. After right unilobar TARE, mean volume of the left lobe increased from 368.26 to 436.16 mL, while the mean volume of the right lobe decreased from 1576.22 to 1477.89 mL. The median KGR of the left lobe was 0.28% per week. The radiation dose absorbed by the healthy parenchyma of the right lobe was significantly higher in patients with increased KGR (31.62 vs. 18.78 Gy, p = 0.037). Linear regression analysis showed that the dose absorbed by healthy parenchyma was significantly associated with increased KGR (b = 0.014, p = 0.043). Conclusion Patients who received right unilobar TARE for liver malignancies could develop a substantial contralateral hypertrophy, and the radiation dose absorbed by the healthy parenchyma of the right lobe was significantly associated with increased KGR in the left lobe. TARE could have a role for inducing contralateral hypertrophy as it offers the advantage of concurrent local tumor control along with its hypertrophic effect.