Background: In the past decade, Tri-Service General Hospital has trained many actors-background standardized patients (SPs). However, we also have recruited some nonactor SPs since 2010. Reviewing the literature, the reliability of SPs with or without actor background would be the impact factor on high-stakes OSCE has not been well studied. Aim: The purpose of this retrospective observation is to clarify whether a SP with or without a professional actor background will affect the performances of the examination when participating in the Taiwan high-stakes objective structured clinical examination (OSCE). The result will be the policy for selecting which kind of SPs to participate in the high-stack OSCE in our hospital. Methods: In this retrospective observation, we analyzed 74 actor background SPs (A-SPs), and 70 no actor background SPs (NA-SPs) who have participated in each spring test of 2015–2017 Taiwan high-stakes OSCE. The data of SPs performance have come from two parts: one is from the examinee with the global rating of the SPs performance and the other is from the examiner with eight-item checklist for the SPs performance. The scoring of both examinee and examiner is a five-point Likert scale. Results: The results show that there is no significant difference in SPs performance from the examinee scoring in the subsequent 3 years, stable and satisfactory, and let examinees feel like real patients. The scores from examiners also showed that two groups of SPs performed equally well without significant differences. Their performance is reliable and consistent, simulating to be a real patient in both groups. However, only one interest finding, when compared to the different age subdivision of SPs, showed the aged subgroup of A-SPs and NA-SPs with the significant difference in the item of reliability and consistent (4.67 ± 0.53 vs. 4.41 ± 0.50, P < 0.05), the possible reason is related to the less-experienced associate with mild memory decline in aged NA-SPs. Conclusions: Our observation gives the essential information, that the well-trained and experienced SP are necessary for participating in the high-stakes OSCE examination, even without the background of the actor. What we need is a professional SP who not only has excellent professionalism but also has a good personality literacy to engage in his/her work.