Recently, many investigations have shown that functionalization of carbon nanotube (CNT) with porphyrin or its metal complex is an efficient way to widen its application areas. As its structural counterparts, boron nitride nanotube (BNNT) exhibits strikingly different properties. In this work, through density functional theory calculations, we report the first study on the functionalization of an (8,0) BNNT with several metalloporphyrin complexes MP (M = Fe, Co, Ni, Cu, and Zn). The results show that adsorption of the MP complex on the N site is the most energetically preferable and the binding energy ranges from 0.17 eV (NiP) to 0.91 eV (FeP). Upon the FeP adsorption, the sp(2) hybridization of the adsorbed N atom is converted to sp(3) hybridization, while the hybridization of the N atom is not changed for the adsorption of other MP complexes. Moreover, the ground state of the BNNT-FeP is predicted to be low-spin (S=0), although the intermediate-spin (S=1) state is the most stable state of the free FeP complex. Finally, the effects of the adsorption of the BNNT by these MP complexes on electronic and magnetic properties of the pure BNNT are further elucidated. (C) 2009 Elsevier B.V. All rights reserved.