The objectives of this study were to find out the 21st century skills and the skills quotient of Principals in Nakhorn Nayok public schools based on self-assessment and peer assessment by their Department heads and to find out if there is correlation of the self assessment and the assessment done by the Department heads. Respondents of this study are ten Principals and 67 Department heads. Random sampling was used in the study. This study utilized Descriptive method. The instrument utilized for gathering the data was an adopted questionnaire from the National Association of Secondary School Principals (www.nassp.org), but translation to Thai language was done to suit the respondents and was tested for its validity and reliability. The data were statistically analyzed and interpreted through basic statistics, such as frequency, percentage, and mean; and inferential statistics, such as Pearson's correlation coefficient (Pearson r), t-test for significant difference of the self and peer assessment. Findings revealed that Principals in Nakhorn ayok schools have high 21st skills quotient based on self-assessment (4.57) and Department heads assessment (4.49). Specifically, it was also found out that there is no difference in the self assessment in the following indicators: setting instructional direction (t[subscript 0.05] = 0.95), teamwork (t[subscript 0.05] = 0.48666), sensitivity (t[subscript 0.05] = 1.0409), development of others (t[subscript 0.05] = 1.614), and results orientation (t[subscript 0.05] = 0.95). However, it was found out that there is a difference in the following indicators: oral communication (t[subscript 0.05] = 4.097), judgment (t[subscript 0.05] = 0.643885), organizational ability (t[subscript 0.05] = 2.63), written communication (t[subscript 0.05] = 4.097 ), and understanding strengths and weakness (t[subscript 0.05] = 3.95). Using Pearson's correlation, it was found out that there is a high correlation (r[subscript 0.01] = 0.468) at 0.01 level of significance between self and peer assessment of the 21st century skills of Principals. Therefore, the indicators with significant difference on self evaluation and Department head's evaluation should be st given attention. There should be capability building for enhancement of the 21st century skills of the Principals.