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— In this work, an electrochemical sensor based on a poly threonine modified graphite-carbon nanotube paste electrode was developed for the investigation of tyrosine. The modification of the electrode was characterized by field emission scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The modified electrode shows many advantages such as simple preparation, good sensitivity, short response time, good stability and reproducibility. The developed electrode was highly selective because of the determination of tyrosine in the presence of the ascorbic acid and the uric acid. Under optimal conditions; the cyclic voltammetry provides a linear response with the concentration range from 2 × 10 –6 to 2.5 × 10 –5 M and 3 × 10 –5 to 1.2 × 10 –4 M with the limit of detection and limit of quantification values of 2.9 × 10 –7 and 9.6 × 10 –7 M. The developed sensor was employed for tyrosine detection in pharmaceutical sample, recoveries obtained were in a range of 99.0 to 102.80%.