Using asphaltenes of two heavy crude oils as examples, it is shown that the pattern of occurrence of asphaltene flocculation and precipitation processes concurs with the difference in the content of A1 and A2 asphaltene fractions and the structural peculiarities of these fractions. It is shown that flocculation and precipitation are usual for fraction A1, but not typical for fraction A2 at identical n-heptane/toluene ratio. The difference in the molecular structures of A1 from A2 consists in greater aromaticity, lower content of side alkyl chains and heteroatoms, and higher molecular weight.