Gambier production in Indonesia comes from smallholder plantations. West Sumatra Province is the leading producer of gambier, with a supply of around 80-90 per cent of the total national gambier production. Based on empirical data, when the selling price of gambier exports increases or fluctuates, the selling price of gambier farmers does not increase as much as the price increase at the level of exporter traders. This condition creates marketing inefficiency. The monopoly index (MPI) is one way to measure marketing efficiency based on the performance of each marketing agency. In this regard, the current business environment is also affected by the Covid-19 pandemic. This study analyzed the monopoly level on the Gambier marketing channel in West Sumatra during the covid 19 pandemic. A survey was conducted in this study. The type of data used in this research is cross-section data. Respondents in this study were gambier farmers, gambier traders, and gambier exporters in Padang City, Lima Puluh Kota, and Pesisir Selatan Regency. The analytical method used in this study is using the Lerner index. Based on the analysis of the monopoly index, it is known that exporters have an enormous monopoly index value compared to other marketing institutions, where the collecting trader has a monopoly index of 4.84, inter-regional traders have 2.09, and exporters have 12.81 MDI. These values showed that exporters dominate gambier marketing in West Sumatra Province. The strong position of exporters in determining prices and marketing gambier is also influenced by cooperation with inter-regional traders (IRT).