Marketplace selection is of critical importance for the success of businesses and more than one criterion should be taken into consideration in this process. There are various multi-criteria decision-making studies in this field. In today’s world, commerce has become electronic and the concept of e-commerce has developed and marketplace selection is also needed for e-commerce. Since there is a lot of uncertainty and complexity in e-commerce marketplace selection and there are some linguistic criteria, it is considered suitable for the fuzzy logic approach. Various fuzzy numbers are used in multi-criteria decision-making problems. There are some studies in the literature on Pythagorean fuzzy numbers, what is one of the fuzzy set extensions. This study will solve the e-commerce marketplace selection problem, which is a multi-criteria decision-making problem, by using the trapezoidal Pythagorean fuzzy TOPSIS method. No such study has been found in the literature. In this respect, the study will be a first in the literature.