The aim of this study is to develop a valid and reliable assessment tool to determine the perceptions of preservice teachers about competency of the 21st century skills. The sample of the sample consisted of 5396 first, second, third, and fourth-year preservice teachers who were studying in different departments at the Faculties of Education of Dokuz Eylül, Fırat, Kilis 7 Aralık, Tokat Gaziosmanpaşa, Burdur Mehmet Akif Ersoy, İnönü, Kahramanmaraş Sütçü İmam, Nevşehir Hacı Bektaş Veli, and Dicle Universities in the 2020-2021 academic year. The study was conducted in accordance with the survey model. As a result of the exploratory factor analysis, it was determined that the scale accounted for 64.43% of the total variance and formed a 3-factor structure consisting of 44 items. The structure of the scale was confirmed with the fit indices obtained as a result of the first and second level confirmatory factor analysis (chi-square/degrees of freedom= 5.04, root mean square error of approximation= 0.041, comparative fit index= 0.91, non-normed fit index= 0.91, square root of standardized residual means= 0.042). In order to determine the reliability of the scale, Cronbach’s Alpha coefficient was calculated on the exploratory and confirmatory factor analysis sample group and it was determined that the Cronbach’s Alpha coefficients of the overall scale and its sub-dimensions varied between 0,84 and 0,96. As a result of the test-retest analysis of the scale, the correlation coefficient between the first and second applications was determined as 0.93 for the total score of the scale; whereas, it was determined as 0,94 for the first factor, 0,83 for the second factor, and 0.94 for the third factor. Results of the study have indicated that the scale of perceptions of 21^st century skills competency is a valid and reliable assessment tool.