The present invention relates generally to a gear backlash compensation mechanism for rack and pinion. Accordingly, the gear backlash compensation mechanism in rack and pinion for accurately positioning carrier drive means along a linear path on a machine which having a linear rack comprising a reversible rack and pinion gearing with drive means for anti-backlash operation, the gear backlash compensation mechanism (10) includes: a) at least one drive head assembly (20) having a pair of reversible pinion gears (30a, 30b), b) a drive gear (40) in associated with a drive means (50), and c) adjustment members (60a, 60b and 60c) configured in communication with the reversible pinion gears (30a, 30b) and the drive gear (40); wherein the reversible pinion gears (30a, 30b) are adapted to engage with gear rack (70) on a machine bed with zero backlash through adjustment members (60a, 60b); and wherein the drive gear (40) is adapted to engage with the pair of the reversible pinion gears (30a, 30b) with zero backlash through the adjustment member (60c).