The simple suspension method has been developed for performing tubal administration by placing tablets or capsules in hot water (55 °C) and serially decaying/suspending them without crushing/opening them. However, the stability of a cardinal drug against the pH of the suspension and heat remains unclear. In this study, we examined the stability of an oral anti-tumor preparation, capecitabine tablets, against the pH of the suspension and heat. Initially, we assessed the stability of capecitabine tablets suspended in phosphate-buffered saline at various pHs. Subsequently, we investigated the stability of capecitabine tablets suspended in phosphate-buffered saline heated at 25 or 55 °C. In addition, we evaluated the stability of this preparation heated at 55 or 80 °C for 30 minutes after being suspended in phosphate-buffered saline heated at 25 °C. When capecitabine suspension was heated at 80 °C for 30 minutes under acidic conditions, the residual capecitabine rate was approximately 50％. Then, a tube passage test of capecitabine was conducted. Passage was favorable. There was no decrease in the content after passage in comparison with the pre-passage value. Based on these results, the tubal administration of capecitabine should be performed considering both the drug suspension pH and temperature.