Excessive usage of electronic devices delays bedtime and increases nighttime arousal, reducing sleep duration of adolescents in the morning shift. The impacts of media use before bedtime (MBB) on sleep patterns and components of morning attention were evaluated in 89 adolescents (15.8 ± 0.8 years) using sleep questionnaires and a continuous performance task. Multivariate multiple regression analysis was used to examine relationships of MBB, chronotype, and gender with sleep and attention. Smartphones were found to be the most frequently used device before bedtime. Attention components were found to be significantly associated with MBB, with a higher frequency of MBB predicting slower reaction times for tonic and phasic alertness and less stable performance of sustained attention. Media usage before bedtime was not significantly associated with patterns of sleep nor sleep quality. This study showed negative impacts of MBB on most components of morning attention, potentially leading to compromised learning in adolescents.