In this study, the applicability of functionalized carbon nanotubes (CNTs) as an additive to increase ethanol heating value has been examined. CNTs were grown within pores of anodic aluminum oxide (AAO), fabricated at the voltages of 40 V and 60 V. Accordingly, CNTs with tubular and Y-branched structures were obtained. Then, CNTs were carboxylated in 10 ppm solution of ethanol and its heating value was examined. Results indicated that Y-branched CNTs only lead to 0.1% increase in ethanol heating value. Tubular CNTs with 16 nm wall thickness raised heating value up to 0.38%. Therefore, Y-branched CNTs resulted in lower increase in ethanol heating value than tubular CNTs. In order to enhance the heating value of this sample, the amine groups including butylamine, dodecylamine, and octadecylamine were used to functionalize the related CNTs. The results showed that the heating values of 10 ppm solutions of functionalized CNTs are higher than pure ethanol about 0.65–2.4%. Moreover, the highest heating value belonged to the solution containing CNTs functionalized by Octadecylamine. Various concentrations of these functionalized CNTs showed that they were stable in 80 ppm ethanol solutions and their heating value and octane number increased by 6.4% and 7.8%, respectively.