Matrix acidizing of the oil wells is one of the most important stimulation techniques for enhancing oil production. The most common acids are hydrochloric acid (HCl), used primarily to dissolve carbonate minerals, and mixtures of HCl and hydrofluoric acid (HF) used to attack silicate minerals such as clays and feldspars. During acid stimulation treatment, the lines and tubing must be protected from corrosive attack by the acid. Among different approaches for mitigation of corrosion, inhibitors are the best to prevent destruction or degradation of metal surfaces in corrosive media. Although many synthetic compounds show inhibitive action, most of them are toxic. There is increasing concern about the toxicity of corrosion inhibitors in petroleum industry. Therefore, finding natural occurring substances as a corrosion inhibitor is subject of great practical significance. A few studies have investigated corrosion inhibition of henna extract on some metals such as aluminum, iron, zinc, and nickel in acidic and alkaline solutions, but, in these studies, henna extract evaluated only for its ability to control acid corrosion under stimulated treating conditions. Formation damage may result from insoluble materials in the inhibitor and from inhibitor adsorption on clays and other minerals present in the matrix of the rock is seldom considered. The purpose of current study is to investigate the side effect of henna extract as a new and ecofriendly corrosion inhibitor on reservoir rock grains. In present work, the inhibitive action of henna extract on corrosion of N80 API steel in HCl 10 wt% at was investigated through electrochemical techniques. The side effect of this inhibitor on rock grains was investigated through linear acid core flooding of calcareous sandstone samples. The analysis of pressure data from the test revealed that the core samples flooded with inhibited acid (HCl 10 wt% containing 0.4 g/l henna extract) have higher pressure drop respect to samples flooded with blank acid (HCl 10 wt%). The results of wettability analysis reveal that samples flooded with inhibited acid have higher contact angle respect to samples flooded with blank acid. It means that henna extract tends the samples toward the oil wet phase.