This paper studies a dynamic model of eco-product planning, where an eco-product supplied by a single producer is differentiated from a conventional product generating negative externalities, and the production technology of the eco-product is characterized by learning-by-doing. The result states that the learning effect causes the eco-product to be more promoted and brings about more favorable outcomes on social welfare. This study also examines how the environmental regulation on the conventional product, associated with a price distortion, affects the promotion of the eco-product, consumer surplus, the single producer's profit, and negative externalities. It is shown that the impact of the environmental regulation is similar to that of a rise in the learning effect. Furthermore, whether or not the environmental regulation should be adopted is highly dependent on the degree of the learning effect. In the presence of a large learning potential, the environmental regulation may not only promote the eco-product effectively but also improve social welfare through intensifying the learning effect.