Eco-driving is an efficient and economical way to reduce vehicles' energy consumption. Eco-driving techniques have been practiced for decades. However, only conventional vehicles have been deeply studied particularly by using optimization and modelling to identify the best energetically speed profiles. In this paper eco-driving of hybrid vehicles is addressed. The complexity of speed profile optimization problem is increased as we have to consider the two energies consumed onboard i.e. fuel and electricity. Considering an existing HEV with its own energy management strategy, we propose here an original approach based on dynamic programming, vehicle modelling and an equivalence factor between the consumed fuel and electricity. Results show that the defined factor should be carefully chosen in order to perform the best fuel economy.