This study aims at searching for evidence of validity of an original scale assessing digital reading metacognitive knowledge developed for PISA 2018, more precisely to investigate whether this scale measures metacognitive knowledge related to reading rather than to digital technological literacy. Data from the 37 OECD countries have been used. The results of the correlations show that the assessment of how several strategies are appropriate to deal with a suspicious email is strongly correlated with reading performance and with the two existing scales of reading metacognitive knowledge. The new scale is also significantly correlated with students’ interest towards reading, their self-concept and self-efficacy in reading, and, on the contrary, is not correlated with their use of digital devices, interest and perceived self-efficacy in using digital devices. The results provide evidence that the new scale assesses digital reading metacognitive knowledge rather than digital literacy, and also demonstrate the strong correlation of this new scale with reading proficiency.