Animal models for the study of erectile function monitoring the changes in intracavernous pressure (ICP) during penile erection was reviewed. The development of new models using small commercially-available experimental animals, rats and mice, in the last decade facilitated in vivo investigation of erectile physiology. The technique enabled to evaluate even subtle erectile responses by analyzing ICP and systemic blood pressure. Moreover, the method has been well improved and studies using conscious animal models without the influence of any drug or anesthesia are more appropriate in exploring the precise physiological and pharmacological mechanisms in erection. Also, more natural and physiological sexual arousal instead of electrical or pharmacological stimulation is desirable in most of the studies. This article reviewed the development of ICP studies in rats and mice.