This study aims to examine the impact of trust and marketing mix (product, price, place, and promotion) on the firms' purchase decisions of palm oil seeds. To meet such aim, we carried out a purposive sampling to obtain the respondents of palm oil firm in West Sumatera. After 82 respondents obtained, to tell on which variables could affect the firms' purchase decisions of palm oil seeds we performed PLS-SEM. The findings showed that marketing mix comprising product, price, place, and promotion could significantly affect the purchase decisions of firms in West Sumatera on palm oil seeds after mediated by trust. Based on the findings, this study may provide insights for the firms of palm oil seeds in a way to increasing their customer purchase decisions.