People conceptualize both time and numbers as unfolding along a horizontal line, either from left to right or from right to left. The direction of both the mental timeline (MTL) and the mental number line (MNL) are widely assumed to depend on the direction of reading and writing within a culture. Although experimental evidence supports this assumption regarding the MTL, there is no clear evidence that reading direction determines the direction of the MNL. Here we tested effects of reading experience on the direction of both the MTL and MNL. Participants read English text either normally (from left to right) or mirror-reversed (from right to left). After normal reading, participants showed the space-time associations and space-number associations typical of Westerners. After mirror reading, participants’ space-time associations were significantly reduced but their space-number associations were unchanged. These results suggest that the MTL and MNL have different experiential bases.