The study aimed to describe the effect of an oral health education intervention on oral hygiene status and gingival inflammation among persons with HIV attending two comprehensive healthcare centres in Nairobi, Kenya. This was a quasi-experimental study of 195 participants (with 102 in the intervention group, and 93 serving as the control group) who were selected using stratified random sampling. The data were collected at baseline, at three months (review 1), and at six months (review 2) using an interviewer-administered World Health Organization clinical examination form. The prevalence of plaque among the participants in the intervention decreased from 70.6% to 18.6%, with a significant decrease in their mean plaque score, from 0.89 to 0.15. The prevalence of gingival inflammation in the intervention group decreased from 58.2% to 12.7%, with a significant decrease in the mean gingival score, from 0.66 to 0.11. No significant change in degree of oral hygiene and gingival inflammation was observed among the non-intervention group. There was a strong association between the change in the mean gingival score and the change in the mean plaque score between baseline and at six months for the intervention group. The regression analysis yielded a coefficient of determination (r2) of 0.76; therefore, 76% of the variation in change in gingival score was explained by the variables in the equation. Only the change in mean plaque score was a significant predictor of the change in gingival score.