Performance Appraisal is a tool for performance improvement. It is an essential human resource activity intended to increase efficiency and productivity and provide an opportunity to continuously review agreed-upon targets as per the organization's set objectives. The objective of the study was to investigate the influence of performance appraisal on the application of professional knowledge, time management, creativity in teaching, and professional development on the performance of public secondary school teachers in Migori County, Kenya. Goal-setting theory guided this study. A descriptive survey design was used. The sample size included 342 teachers from 57 schools. The study used simple and stratified random sampling techniques. Questionnaires and a document analysis guide were used to collect data. Content validity was tested through expert judgement by the supervisors. The test re-test method was used to test reliability. The reliability of the questionnaire instrument was 0.85. Data were analyzed using ANOVA, Pearson correlation coefficient ('r'), and multiple Regression analysis. The study established that Teacher performance appraisal is a significant predictor of teachers' performance. The study concludes that teachers' performance appraisal translates into efficiency and increased productivity. The study recommends, among others, that performance expectations of the teacher should clearly be communicated to them by the Teachers Service Commission (TSC) and that teachers should be involved in designing performance appraisal criteria.