<p>In practice, many products are produced and stocked as product lines rather than as single product variants. However, due to the impact of product differentiation, demand uncertainty, and expanding costs, the manufacturer and retailer usually do not agree on the length of the product line, especially when the supply chain (retailer) faces capital constraints. The focus of this research, therefore, is studying how product line length and supply chain operation decisions depend on the retailer’s financing strategy (bank credit and trade credit) and product differentiation. We present a game-theoretic model comprised of a manufacturer who sells one product or two differentiated products through a capital-constrained retailer. When either or both bank credit and trade credit are viable, we analysed the coupling effect between product line length, product differentiation and the financing equilibrium. We find that a manufacturer’s optimal product line design strategy is selling two differentiated products (single products) when the product differentiation is relatively low (high). When the product differentiation is moderate, the optimal product line length is dynamic and changes with the financing strategy. Our study contributes to the growing body of literature on product line design and supply chain finance. Several managerial implications for supply chain operations also emerge from the study.</p>