This research studies quality of atmosphere dominant on brother-sister relation of offsprings in Isfahan families. This is descriptive research and statistical population is all 15-25 year old single offsprings in Isfahan Province. After statistical estimation and determination of required sample, 220 families were selected using multi-stage cluster sampling and considered sample was chosen from single offsprings. Research instrument were index of brother-sister relation (IBR) questionnaire which was provided by Walter, Hudson, Gordon MacNeiland Walmir and have had appropriate validity and reliability in previous researches. In order to data statistical analysis, descriptive and deductive analysis methods such as cut point, t-test, comparison of two independent groups’ mean, and one-way analysis of variance (ANOVA) F test were used. Main findings of the study include: 47.8% of family offsprings in Isfahan did not describe brother-sister relation appropriate and desirable. Calculated t in level of P≤ 0.05 showed meaningful difference in description of atmosphere dominant on brother-sister relation described by boys and girls. Boys have described this atmosphere more inappropriate and undesirable than girls and this difference is statistically meaningful. Calculated F in level of P≤ 0.05 did not show meaningful difference between families offsprings’ comments on atmosphere dominant on brother-sister relation based on variable of location of life. F calculated in level of P≤ 0.05 explained meaningful difference between families offsprings’ comments on atmosphere dominant on brother-sister relation based on variable of age.