Pre-hypertension means borderline hypertension and if unchecked can lead to hypertension and its other consequences. Stressful occupations such as market trading can predispose persons to hypertension disorders due to long work hours, little or no rest and this raised concern for pre-hypertensive traders’ routine and their health status. Studies have shown benefits of health-education intervention in enhancing appropriate hypertension prevention information. However, this is limited in Nigeria. Therefore, this research assessed knowledge level of hypertension among pre-hypertensive market traders in Lagos State. Two major markets were surveyed to obtain sample size of 140 traders. By voluntary participation, the pre-hypertensive traders were grouped per market into Intervention Group (IG: 70) and Control Group (CG: 70). The IG was assigned to 6-weeks health education modules on hypertension once weekly for 15 minutes and CG had placebo for same duration. Research instrument with reliability coefficient (0.79) was used to collect data. Response rate was 98.6%. Data were analysed at 5% level of significance. Findings showed the baseline, mean score of knowledge in the IG was 15.37 ± 5.20, and for CG was 15.33 ± 3.93. Comparing the baseline and immediate post-intervention, there was a significant difference in the knowledge mean scores of participants in the IG (20.04 ± 1.54), but, there was a slight decline in the CG 15.32 ± 3.88 at p > 0.05. In conclusion, health-education intervention had positive influence on hypertension-related knowledge of pre-hypertensive traders in Lagos State. It was recommended that health workers should adopt regular market-based health-education programs to promote hypertension prevention