A fluxgate magnetic sensor consists of a solenoid excitation coil, pick-up coil, and magnetic core. We presents the effect of magnetic core shape in a micromachined fluxgate sensor. To observe the performance of fluxgate sensor with magnetic core side width and gap, side width of 125 ${mu}{ extrm}{m}$, 250 ${mu}{ extrm}{m}$, and 500 ${mu}{ extrm}{m}$ were designed in a rectangular-ring shaped core and the gaps of 0 ${mu}{ extrm}{m}$, 50 ${mu}{ extrm}{m}$, and 100 ${mu}{ extrm}{m}$ were also fabricated in a racetrack shaped core. The solenoid coils and magnetic core were separated by benzocyclobutane(BCB) which had high insulation and good planarization characters. Copper coil patterns of 10 ${mu}{ extrm}{m}$ width and 6${mu}{ extrm}{m}$ thickness were electroplated on Ti(300 $AA$) / Cu(1500 $AA$) seed layers. 3 ${mu}{ extrm}{m}$ thick N $i_{0.8}$F $e_{0.2.}$(permalloy) film for the magnetic core was also electroplated under 2000 gauss to induce the magnetic anisotropy. The magnetic core had the high DC effective permeability of ∼1,300 and coercive field of ∼0.1 Oe. Because the magnetic cores of 500 ${mu}{ extrm}{m}$ side width and 0 gap had a low magnetic flux leakage, high sensitivity of ∼350 V/T were measured at excitation condition of 3 $V_{P-P}$ and 2 MHz square wave. The power consumption of ∼14 ㎽ was measured. The fabricated fluxgate sensor had the very small actual size of 3.0${ imes}$1.7 $ extrm{mm}^2$. When two fluxgates were perpendicularly aligned in terrestrial field, their two-axis output signals were very useful to commercialize an electronic azimuth compass for the portable navigation system.m.m.m.