In the present study to analyze the role of ACTH in fetal tissues and organs, we observed the expression of melanocortin type 2 (MC2) and 5 (MC5) receptors in ICR mouse embryos from E11.5 to E18.5 by immunohistochemistry. In the adrenal gland and testis, both receptors were expressed from E13.5 to E18.5. In the genital ridge and the ovary, melanocortin type 2 receptors (MC2R) was detected from E11.5 to E12.5 and from E13.5 to E18.5, respectively, while melanocortin type 5 receptors (MC5R) was not detected. In the mesonephros, MC2R and MC5R were expressed from E11.5 to E12.5, and in the metanephros, MC2R and MC5R were expressed from E12.5 to E18.5 and from E14.5 to E18.5, respectively. In the lung, MC2R was expressed from E11.5 to E14.5, but MC5R was not expressed at all. In blood cells, MC5R was detected at all stages examined, while MC2R was detected at none. MC2R was observed in the brain and spinal cord from E11.5 to E13.5, while MC5R was detected only in the telencephalon and only from E16.5 to E18.5. At different temporal patterns, MC2R, but not MC5R, was detected in the choroid plexus, while MC5R, but not MC2R, was expressed in the liver and in the nasal epithelium, and both MC2R and MC5R were expressed in the dorsal root ganglion and the trigeminal ganglion. These findings show the spatio-temporal specific expression patterns of MC2R and MC5R in the mouse embryo and suggest that ACTH may be related to histogenesis and/or prenatal function of various tissues and organs via MC2R and/or MC5R.