The potential energy surface for the reaction of diborane B2H6 with ammonia has been calculated by MP4/ 6-311 + G(d,p)//MP2/6-31C(d,p) method with zero-point energy corrections. Two steps for the formation of aminoborane, H2B=NH2 were studied. The first step is the formation of borane-ammonia adduct H,B : NH3 and complex H3BHBH2NH3, and the second is three type (1,1-, 1,2- and 1,3-) subsequent hydrgoen eliminations. The adduct H3B:NH3 formation occurs via the dissociation (BH3 + BH3) of diborane or via the complex H3BHBH2NH3 formation. Two transition states for the complex H3BHBH2NH3 formation from diborane and ammonia were found, which are an ionic and a covalent (keeping of one B-H-B bridge bond) types. The transition state of the covalent type is about 5 kcal/mol lower in energy than that of the ionic one. For I,l-hydrogen elimination, two eliminations from B atom and from N atom of H3B:NH3 are examined. The energy barriers for both eliminations are extremely high (107-103 kcal/mol from the isolated diborane and ammonia). For 1,2-hydrogen elimination, four reaction paths were calculated. These reaction paths have also high energy barriers (33-46 kcal/mol), since essentially they are forbidden reactions by the Woodward-Hoffmann rules. The reaction pathway of 1,3-hydrogen elimination includes two concerted reactions (hydrogen elimination and hydrogen shift), which have a low energy barrier of 16.7 kcal/mol at the MP4/6-311+G(d,p) + ZPE level. Two elimination pathways (1,2-hydrogen elimination from the adduct and 1,3-hydrogen elimination from the complex) lead to aminoborane in one step, except for 1,1-hydrogen elimination with extremely high barrier.