<p>DD3R zeolite, a potential adsorbent for CO₂, is generally synthesized by hydrothermal process, which involves the nucleation from precursor sols or the conversion of reactive gels into zeolite crystals. However, DD3R zeolite synthesis typically requires prolonged synthesis times, even at elevated temperatures. Addition of seed crystals can reduce synthesis time and inhibit impurity phase formation; however, the effect of seed crystals on zeolite crystallization is not completely elucidated thus far. Accordingly, we investigated the role of seed crystal structure in seed-assisted method and attempted to understand its crystallization acceleration mechanisms. Here, CHA, DD3R, ETL, MFI, and FAU were used as seed crystals to synthesize DD3R zeolites. Only DD3R and CHA seeds facilitated the crystallization of the DD3R zeolite. In addition to the conventional hypothesis of composite building units (CBUs), the results propose another hypothesis based on the difference between lattice constants and crystal plane structure similarity of the crystalline phase of seed crystals and the product zeolite, i.e., hetro-epitaxial growth. The large difference between lattice constants and structure of ETL, MFI and FAU against DD3R did not promote crystallization of DD3R, whereas the similarity in lattice constants and structure of CHA facilitates its crystallization, even in absence of common CBUs.</p> Graphical Abstract <p></p>