The combination of skin external preparation and transdermal patch is influenced by drug absorption through the skin. We investigated the effect of heparinoid cream on the transdermal absorption of oxybutynin hydrochloride using an oxybutynin transdermal patch and determined the combined effect of these medications. Normal skin and dry dorsal skin in hairless mice were treated with heparinoid cream, followed by the application of the oxybutynin transdermal patch. A blood sample was collected from the mouse tail vein and the blood concentration of oxybutynin hydrochloride was analyzed by LC-MS/MS. Transepidermal water loss, the hydration level of the stratum corneum, and the stratum corneum thickness in the dorsal skin were measured. The blood concentration and area under the curve (AUC)_0→24 of oxybutynin hydrochloride increased when the 4.0-cm² oxybutynin transdermal patch was applied 1 h after the application of the moisturizer, compared to the values without moisturizer. Normal skin and dry skin did not affect this result. As the hydration level of the stratum corneum and stratum corneum thickness increased before patch application by pre-treatment with moisturizer, it was suggested that transdermal absorption of oxybutynin hydrochloride was increased by skin hydration. The increased blood concentration of oxybutynin hydrochloride was regulated by changing the effective area of the patch and applying additional moisturizer at intervals. The pharmacokinetics of oxybutynin hydrochloride under the regulation of combination treatment was similar to that of treatment without moisturizer. These findings indicate that the application conditions of the oxybutynin transdermal patch and heparinoid cream influence the proper use of the patch.