The MgB 2 tapes fabricated by the in-situ powder in tube (PIT) technique were investigated with respect to the relationship between the starting powder(s) and the critical current density, J c . A powder of MgB 2 or a mixture of Mg and B (Mg+2B) powders was added to the mixture of MgH 2 and B (MgH 2 +2B) powders in a ratio of x:(1−x). The amount of x was controlled from 0 to 1, and the synthesis condition were 600°C for 1h in Ar gas. The J c at 4.2K and 10T of the MgB 2 tape systematically depend on x for both MgB 2 and (Mg+2B) additions, but the trends are not the same. The dependence of the J c on x for MgB 2 addition peaks at around x=0.3 (J c =4.3×10 3 A/cm 2 ), however the (Mg+2B) addition monotonically degrades J c . The cross-sectional image observed by scanning electron microscope shows that the MgB 2 addition clearly densifies the tape core. On the other hand, the amplitude dependence of the AC magnetization curves shows that grain coupling of the tape core is unchanged or slightly improved by MgB 2 addition, but degraded by (Mg+2B) addition. Therefore, we conclude that the enhancement in J c by an appropriate amount of added MgB 2 is due to optimization of densification and degradation of the grain coupling between MgB 2 grains in the tape core.