The aims of the study are to construct an online instrument to assess different aspects of morphological awareness and to examine its development and its relation to reading comprehension in grades 2-4 in Hungarian children. Altogether, 4134 students were tested. The online test evaluated inflectional, derivational, and compound morphological skills with five subtests. The instrument proved to be reliable. CFA examinations revealed that the five subtests were empirically distinguishable dimensions. Inflectional, derivational, and compound morphology as the three main dimensions of morphological awareness were also empirically supported by our data. Morphological awareness skills improved significantly and developed in parallel with reading skills throughout grades 2-4. The increase in the development of morphological awareness from grade 2 to grade 3 tends to be faster than the growth between grade 3 and 4. Positive moderate correlations were found between morphological skills and reading comprehension and the relationships seem to be stable throughout the three grades. The most significant predictor of reading comprehension is the Affix Identification for Nonwords subtest. Our study showed that morphological awareness could be assessed efficiently through online media and drew attention to the importance of morphological awareness in the development of reading comprehension and linguistic intelligence.