Energy management is one of the key challenges for the development of Hybrid Electric Vehicle (HEV) due to its complex powertrain structure. Hardware-In-the-Loop (HIL) simulation provides an open software architecture which enables rapid prototyping HEV energy management system. This paper presents the investigation of the energy management system for a single shaft parallel hybrid electric vehicle using dSPACE eDrive HIL system. The parallel hybrid electric vehicle, energy management system, and low-level Electronic Control Unit (ECU) were modeled using dSPACE Automotive Simulation Models and dSPACE blocksets. Vehicle energy management is achieved by a vehicle-level controller called hybrid ECU, which controls vehicle operation mode and torque distribution among Internal Combustion Engine (ICE) and electric motor. The individual powertrain components such as ICE, electric motor, and transmission are controlled by low-level ECUs. To examine the performance of hybrid ECU and low-level ECUs, vehicle mode control, speed tracking, energy distribution, regenerative braking, and engine operating region were investigated in the HIL environment with a hardware electric motor controller consisting of dSPACE MicroAutoBox II and the AC Motor Control Solution. The presented work illustrates that the HIL system is a suitable environment for the rapid prototyping of HEV control strategies.