Sarcosine has been identified as a key metabolite marker for monitoring and early diagnosis of metastatic prostate cancer (PCa), and it is detectable in the urine of patients. In the present study, a carbon past electrode modified with TiO2 nanoparticles in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid is proposed for the voltammetric determination of sarcosine in biological samples. Electrochemical impedance spectroscopy was used to study the charge transfer properties of the proposed electrode at the electrode–solution interface. Cyclic and differential pulse voltammetric methods were used to evaluate sarcosine electrochemical behaviour. Electrochemical oxidation of sarcosine on the new TiO2/ionic liquid carbon paste electrode (TiO2/IL/CPE) was carefully studied. The plot of oxidation peak current versus the concentration of sarcosine consists of two separate linear portions. The first part is for 0.1 to 1 mM (direct proportion) and the second one is for 1.0 to 5.0 mM of sarcosine (linear portion). The detection limit was 0.08 mM (3σ) in phosphate buffer (pH 11.5). The measurement and fabrication reproducibilities of the modified sensor were 1.7 and 3.46% for 0.6 mM sarcosine, respectively. The proposed method was successfully applied for the determination of sarcosine in a spiked real sample.