During cavity preparation and the removal of carious dentin, it is possible to happen the exposure of dental pulp accidentally, it named pulp exposure by iatrogenic factor. Pulp exposure can make the irritation of the pulp then causing pulp necrosis. Fibroblast is predominant cell of pulp that involved in degradation process and active during pulp damage. The aim of this study is to know fibroblast cell responses in pulp with exposure condition caused by iatrogenic factor on day 1, 3 and 7. The study was an experimental laboratory research in vivo which used 9 Sprague Dawley male rats was divided into 3 groups base on pulp exposure duration, there was group day-1, day-3 and day-7. Maxillary right molar was given iatrogenic injury by round bur and explore. Number of fibroblast was observed after made of preparat with Hematoxylin eosin. The results showed the average number of fibroblasts in group day 1 more, with a value of 3,67 compared with the group day 3 with the value of 2,33. Average of fibroblast most founded in group day 7 with a value of 13,67. Data from each group were analyzed using normality, homogenity, one-way annova and tukey test. Analysis result on influence of pulp exposure time to number of fibroblast cell of right molar maxillary Sprague Dawley (after mechanic injury) shows result with p value=0,011, Thus, it can be concluded that there is a significant difference between time exposure and number of fibroblast. The conclusion of this study is fibroblast respon of molar Sprague Dawley rat which pulp exposed by iatrogenic day 1, 3, and 7 has significant differentiation statistically with p value <0,05.