Doxorubicin is an anthracycline antibiotics that is used as adjuvant therapy for breast cancer. Doxorubicin will be metabolized to the main metabolite namely doxorubicinol. According to some studies that  had been done, doxorubicinol that accumulates in human body can increase the risk of heart abnormalities or have a cardiotoxic effect. In this study, an analysis of doxorubicin and doxorubicinol in Dried Blood Spot (DBS) sample from 25 breast cancer patients who received doxorubicin in their therapeutic regiments has done to monitoring the toxicity effects of doxorubicinol. DBS samples were extracted by protein precipitation method and analyzed using Ultra Performance Liquid Chromatography tandem Mass Spectrometry (UPLC-MS/MS). This method was linear within the concentration range of 10 – 200 ng/mL for doxorubicin and 4–100 ng/mL for doxorubicinol. The analysis results on 25 breast cancer patients showed that doxorubicin levels were in the range of 11.01 ng/mL to 93.75 ng/mL and doxorubicinol was 5.80 ng/mL to 58.57 ng/mL. Cumulative doses of all patients were in the range of 49,11 mg/m² to  303,70 mg/m²which have cardiomyopathy incidence rates < 4% (cardiomyopathy incidence rates are 4% at 500 to 550 mg/m²,18% at 551 to 600 mg/m², and 36% at >600 mg/m²).