Muslims throughout the world observe dawn to dusk fast in the month of Holy Ramadan. This study aims to investigate the effect of fasting on serum lithium levels in an animal model under typical conditions of Ramadan. Animals were categorized into oral and intraperitoneal groups. Each group was divided into fasting and non fasting groups along with their controls having six animals each. Mean serum lithium levels of non-fasting and fasting rats were assessed. Mean serum lithium levels of oral non-fasting rats was 0.23±0.004 mequiv/L, (n=6) compared to oral fasting rats 0.20+0.002 mequiv/L, (n=6) mean difference=0.003. The mean difference between mean serum lithium level of intraperitoneal non fasting (0.246±0.015 mequiv/L, n = 6) and intraperitoneal fasting rats (0.206±0.020 mequiv/L, n = 6) was 0.02. These differences were statistically non significant (P>0.05). The mean serum lithium is not grossly affected by fasting in rats under 25ºC and fasting for almost 12 hours which is consistent with a previous clinical study. Lithium can be used by fasting bipolar patients but, will require careful supervision.