This article is devoted to analysis of the main methodological problems encountered by scientists in the process of new religious movements monitoring. The main focus is placed on the one of the most difficult kinds of such monitoring, namely analysis of the whole range of unconventional religious groups existing in one or the other country of the world. Three main problems of such monitoring are highlighted: a) the problem of pre-conceptualization of main types of religious groups or objects of monitoring; b) the problem of collecting information about objects of monitoring; c) the problem of analysis of the collected information. The last problem of correct identification of the documents of new religious movements during their analysis is the most difficult one. It is shown that emergence of all those problems is caused to the great extent by specific features of unconventional religiosity itself. Among other causes are: a) diverse patterns of new religious movements geographical distribution; b) extraordinary high level of changeability of practically all their main characteristics, modes of action, and self-representation in society; c) high level of similarity and mutual plagiarism of beliefs and religious practices between different groups of the same type of unconventional religiosity. Every problem is analyzed. Different solutions to each of them are offered on the basis of authors’ 19 years experience of longitudinal monitoring in new religious movements in Republic of Belarus. It is suggested that conceptualization of new religious movements must follow the procedure of their monitoring. Complementary ways of collecting information are proposed. It is shown that development of database management system including about 60 variables of different sides of new religious movements can be one of the solutions to the problem of identifying their documents.