A novel sandwich-type electrochemical aptasensor was designed for ultrasensitive detection of MUC 1 based on the aptamer functionalized semiconducting polymer dots (PS-COOH-co-PFBT Pdots) as the biosensing interface. In this work, rGO-N-'1,N-'3-dihydroxymalonimidamide nanosheets with large surface area, excellent electro-conductivity and good adsorption capacity were not only employed as the ideal carrier to immobilize numerous aptamers but also acted as the sorbent for the accumulation of electroactive thionine (Th). The fast constructed biosensing interface could specifically capture tumor marker MUC 1, leading to assembly of secondary aptamer functionalized rGO-N-'1,N-'3-dihydroxymalonimidamide/Th nanohybride. Consequently, the increase in current intensity of the differential pulse voltammogram of adsorbed thionine was monitored and found to be linearly proportional with increasing concentration of MUC 1 in the range of 0.1-14.5 nM with a limit of detection of 0.06 nM. Additionally, the designed aptasensor showed acceptable selectivity, reproducibility, repeatability and stability. The satisfactory results in analyze human serum samples indicated potential application for clinical monitoring of this tumor marker.