The phases and magnetic properties of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5, and 4.0) are studied by X-ray diffraction analysis and magnetic measurements. Proper addition of Ti could improve the magnetic properties of Co-Zr alloy significantly. The largest value of Hc=7.0 kOe (1 Oe =79.5775 A/m) is obtained in the Co77Zr16Mo5B2 melt-spun ribbon. The grain size of Co5Zr phase decreases with the increase of B content, which contributes significantly to the enhancement of exchange-coupling effect. The coercivity values of the Co77Zr18-xMo5Bx (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are affected mainly by the grain size of the Co5Zr phase. The coercivity value first increases and then decreases with the decrease of the Co5Zr phase. On the other hand, the coercivity mechanisms of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are found to be of the pinning type.