Digital annotation of verbal aspect in Old Russian and Church Slavonic texts is a challenging and quite complicated task that requires a complex approach. While studying Slavic aspect systems synchronically, we always know whether the verb is perfective, imperfective or biaspectual, however, this is often not the case for the research of aspect in a diachronic perspective. The determination of the aspectual status of a particular verb for earlier stages is possible only after considering together different parameters such as: actionality, lexical semantic, morphology, functional distribution, syntactic restrictions, collocations, statistics etc. All essential parameters should be annotated sufficiently for an effective use of a corpora. That would enable a researcher to collect quickly the information necessary to build aspectual profile of a verb. It is also important to understand the hierarchy of the parameters, as they might have different degrees of importance, and for this purpose a special algorithm should be developed. The preliminary results, related to the parameters of annotation and the algorithm for aspect determination (using ‘Morphy’, the System for digital morphological annotation of Old Russian and Church Slavonic manuscripts, developed in Vinogradov Russian Language Institute RAS), are discussed in the paper.