Group‐buying price mechanism is useful for online sales since the 1990s, yet it has not been widely applied in the business‐to‐business (B2B) environment. In this study, we consider a B2B supply chain with one supplier and multiple retailers. With our analytical model, we compare the supplier's profit under the flat price mechanism, individual quantity discount mechanism, and group‐buying price mechanism. The results show that when retailers are homogeneous, the individual quantity discount mechanism is the best choice for the supplier. In situations with heterogeneous retailers (i.e., a large retailer and multiple small retailers), the group‐buying price mechanism is the best choice when there is a moderate difference in market scale between retailers. However, the condition is quite strict. These findings also hold with a step‐wise price menu set by the supplier. Our conclusions explain why the group‐buying price mechanism is not widely used in the B2B environment and provide some advice for the supplier on how to choose suitable pricing mechanisms.