This study was undertaken to establish the different pharmaceutical properties between promethazine HCl and promethazine pamoate. First, promethazine pamoate was prepared by using the modified method of Saias. Second, in order to study the different pharmacokinetics between promethazine pamoate and promethazine HCl, absorption rate, plasma concentration, and distribution, as well as urinary excretion of the both compounds were examined in rabbits as an experimental animal: The results were as follows. 1. In the in vitro isolated intestine of rabbit, the rate constant for absorption of promethazine pamoate was $0.347hr^{-1}$ and that of promethazine HCl was $0.532hr^{-1}$. 2. After oral administration of promethazine pamoate, the increase of plasma concentration of promethazine was much slower than that of promethazine HCl. 3. The urinary excretion rate of promethazine pamoate was significantly low in comparison to that of promethazine-HCl; i. e. about 50% of promethazine HCl was excreted within 3 hours, and 5 to 15 hours for that of promethazine pamoate. 4. The tissue concentration of promethazine after oral administration of promethazine pamoate in rabbit was steadily increased for 5 hours. However, promethazine HCl concentration reached to maximum 1 hour after administration, then decreased slowly. 5. A significant amount of promethazine was mainly distributed in spleen, kidney, lung, liver and heart in this order, rather than other organs, such as brain, and muscle. 6. In the toxicity test by using mouse, $LD_{50}$ for promethazine pamoate was 3,250 mg/kg, while $LD_{50}$ for promethazien HCl was 298mg/kg.