Background: Transcatheter arterial chemoembolization (TACE) is the standard treatment in selected patients with unresectable hepatocellular carcinoma (HCC). Drug-eluting particles are developed to reduce side effects and improve efficacy. We present safety data of a prospective randomized phase II study with doxorubicin-eluting superabsorbent polymer (SAP) microspheres. Material and Methods: We prospectively included 30 HCC patients with different Barcelona Clinic Liver Cancer (BCLC) stages (A = 3, B = 19, C = 8) and randomly assigned them to receive conventional TACE (n = 14) (control group) or doxorubicin-eluting SAP microspheres (n = 16). The doxorubicin plasma level was assessed at different time points, biochemical analysis was performed, and side effects were reported following the Common Toxicity Criteria. Tumor response was assessed at 6 weeks according to the modified Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Results: There was a significantly lower plasma peak concentration (Cmax) of doxorubicin and smaller area under the curve (AUC) with SAP microspheres (mean Cmax 495 ± 293.9 ng/ml, mean AUC 69.7 ± 26.9 ng/ml min) compared to controls (mean Cmax 1,928 ± 560.8 ng/ml, mean AUC 165 ± 32.3 ng/ml/min; both p < 0.001). Furthermore, there were less grade 3 and no grade 4 adverse events in the SAP microsphere group. Tumor response was comparable between the groups. Conclusions: TACE with SAP microspheres leads to low plasma levels of the cytotoxic drug and therefore minimizes toxicity compared to conventional TACE.