In the nucleon-pair shell model truncated to the S-D subspace with single-particle level splitting fully taken into account, the effects on the collectivity due to the pair structure are studied for 134Ba. It is found that the yrast states are not sensitive, but the others, especially the 02+ and 22+ states, are very sensitive to the D-pair structure. Among the lbur pair structures studied in the paper, only the SD pairs taken from the 01+, 21+ states of two-valence-nucleon systems with surface delta interaction can describe the spectra, and the B(E2) and B(MI) values of 134Ba. @ 1998 Published by Elsevier Science B.V.