Several MgB 2 monofilamentary samples are prepared to evaluate the effects that the doping compounds B 4 C, Al 2 O 3 , and SiC have on critical current density ( c ) and the c dependency of magnetic flux density ( ) of the sample. All of the samples in this study have Nb sheaths and are manufactured using in situ precursor powders and the Powder-in-Tube fabrication method. The amounts of added impurities are 10 wt.% for B 4 C and Al 2 O 3 , and 3, 10, and 20 wt.% for SiC. A reference sample without any doping is also prepared. All of the samples are heat treated between 650 and 800 C for 30 minutes. The transport c ( ) characteristics are measured at 4.2 K and the magnetic c ( ) behavior is obtained in varied temperatures up to 30 K.The changes in connectivity, or effective cross-section, are also evaluated by performing resistivity measurements on the samples after removal of the sheath. Furthermore, the pinning forces of the samples are evaluated from the magnetic measurements.Index Terms-Connectivity, current density, heat treatment, impurity addition, magnetic field effects, MgB 2 .