The Self-Regulation for Learning Online (SRL-O) questionnaire was developed to encompass the breadth of motivational beliefs and learning strategies that are often used in online and/or blended learning contexts. No current measure meets all these needs. This study used two non-duplicate samples to provide evidence of the psychometric properties of SRL-O using exploratory factor analyses (sample 1, n = 313), and confirmatory factor analyses, convergent and content validity and reliability (sample 2, n = 321). The SRL-O has a 10-factor structure, made up of (1) online self-efficacy, (2) online intrinsic motivation, (3) online extrinsic motivation, (4) online negative achievement emotion, (5) planning and time management, (6) metacognition, (7) study environment, (8) online effort regulation, (9) online social support, and (10) online task strategies. The SRL-O was also found to have two superordinate factors (motivational beliefs and learning strategies). The SRL-O was demonstrated to be a psychometrically sound measure of online SRL for learners studying in online and blended learning contexts. There is no other online self-regulated learning questionnaire that currently covers such a wide range of motivational beliefs and learning strategies.