Received 10 November 2000; received in revised form 24 January 2001; accepted 27 February 2001 By using top seeding melt-textured growth (TSMTG) process, large single domain YBaz Cu3 07 JY2 Ba Cu O5 (YBCO) samples were prepared with addition of nanometric SnO2 and normal CeOy. Polarized light microscope studies at each step of the TSMTG process showed that before YBa2 Cu3 07 δ (123) melting, the Sn-based reacted products were uniformly distributed in micrometer scale; after solidification, the trapped YyBaCuO5 (211) and Sn-based inclusions were more homogeneously distributed and with mean sizes of about one micrometer. Composition images of scanning electronic microscope for the textured samples showed that, on the whole, the Sn-based inclusions were smaller than the 211. They must be on average below one micrometer in size. Although evidence was found that very fine Sn-based inclusions were uniformly trapped in 123 matrix, the fraction of them was small in comparison to that of 211. No significant enhancement of superconducting critical current density (Jc) was evidenced for the nanometric SnOy-doped samples at a low magnetic field (B<1 T). However, values of Jc were decreased at intermediate magnetic field (1<B<3 T). 2001 Elsevier Science B.V. All rights reserved.