The purpose of this study is to develop a valid and reliable scale to measure e-consumers' attitudes towards ethically questionable online behaviors (e-CEQOB). A scale measuring e-consumers' attitudes towards such behaviors was developed using the conventional steps of scale development of Churchill (1979). The generated items were reduced to 24 items following EFA. The psychometric properties of e-CEQOB were assessed on two independent non-student samples in Istanbul, Turkey (Sample 1, N=635, and Sample 2, N=880 - randomly split into two (G1, n=438, G2, n=442)). The e-CEQOB scale was statistically confirmed and validated using CFA and Maximum Likelihood Estimation (Lisrel 8.72). As a result of EFA and CFA, a 24-item, five-factor multi-dimensional construct on e-CEQOB was developed and its reliability and validity were tested and confirmed. Taking into consideration the gap in the literature, this study has developed and validated an instrument that measures e-consumers' attitudes towards ethically questionable online behaviors. Although there are a limited number of studies on such, none has attempted to develop a scale using the conventional steps of scale development and none has been tested for validity and reliability, nor has any been widely accepted. This study fills this gap and presents a reliable and valid scale to measure the attitudes of e-consumers towards ethically questionable online behaviors (e-CEQOB). The creation of e-CEQOB serves as an opportunity for researchers studying in this rapidly developing medium to extend their research to critical ethical issues. The applicationof e-CEQOB to different cultures is important for testing its reliability and validity in different cultures in order to improve its validity.