The purpose of this study was to examine the effects of matching supervisors and counselor trainees personality characteristics of introversion/extraversion on supervisory working alliance and basic counseling skill development. The quasi-experimental two-treatment group study was conducted at a large mid-western urban university with master-level counselor trainees and advanced degree supervisors from a CACREP accredited Counselor Education Program during one semester. Fifteen practicum counselor trainees and eight advanced degree supervisors participated in the study. The data included pre-and-post measurements of the dependent variables, supervisory working alliance and basic counseling skill development, measured by the Supervisory Working Alliance Inventory (SWAI) and Basic Skills Observation (BSO) scales respectively. Pre-testing was conducted to determine supervisors and counselor trainees’ personality characteristics of introversion/extraversion using the Myers-Briggs Type Indicator (MBTI) to create the matched/non-matched supervisory dyads. The independent variable was group assignment based on matched/non-matched personality characteristics. A Hotelling's Trace Multivariate Analysis with group membership as the fixed, independent variable and pretest scores serving as the covariates was used to examine the hypothesis. There were no significant differences found for the dependent variables between the two treatment groups. Although the research hypothesis was not found to be statistically significant, the Tests of Between-Subjects Effects by Treatment Group for the BSO pre-and-post data showed α = .04 which indicated something of significance was found. Therefore, a univariate paired samples analysis for both treatment groups utilizing the pre- data as the covariate was conducted. The BSO resulted in a statistically significant level of α = .01 for the Experimental Group (Matched Supervisor/Counselor Trainee Personality Characteristics). The BSO resulted in a statistically significant level of α = .00 for the Comparison Group (Non- Matched Supervisor/Counselor Trainee Personality Characteristics). Reliability was also determined for the BSO.