Background: A high rate of periodontal disease has been observed among Yemeni male qat chewers. This study was performed to evaluate clinically the effect of qat chewing habit on the volume of gingival crevicular fluid (GCF) by (Periotron 8000)®. Subjects and Methods: A total of 120 subjects (80 males) and (40 females) qat chewers patients were involved. They were divided into three groups according to the duration of qat chewing habits (5 years, 6–10 years and >10 years). The plaque index (PLI) and gingival index (GI) were recorded at baseline, 10 days, 15 days, and 20 days intervals. The GCF samples were collected by insertion of absorbent strips subgingivally without contact with gingival tissues 1 mm for 30 s. Periotron 8000® was used for the evaluation of the volume of GCF at baseline, for 1 h, 24 h, 5 days, 10 days, 15 days, and 20 days intervals. The data were collected and analyzed by NOVA test. Results: There were significant differences in the mean of (PLI), GI and the volume of GCF in all patients groups at all intervals of this study. Conclusion: The GI and GCF were increased with duration of qat chewing habit due to increased severity of gingival inflammation whereas the PLI was decreased due to the effect of self-cleansing during qat chewing habit.