Radon and its progeny present in houses and others dwellings represents the most important contribution to dose from natural sources of radiations. The measurements of indoor radon are performed by using passive LR-115 nuclear track detectors calibrated at NIRS, Japan during the 4th International Intercomparison of Radon and Thoron Passive detectors. The values of indoor radon concentration vary from 54.26 Bqm-3 to 141.09 Bqm-3 with an average value of 97.68 Bqm-3. However, the value of effective dose varies from 0.93 mSvy-1 to 2.41 mSvy-1 with an average value of 1.67 mSvy-1. An attempt is made to estimate the effect of ventilation conditions on the annual effective dose due to indoor radon concentration. The dwellings were selected on the basis of different ventilation conditions. The result of the present study indicates that changes of ventilation rate have significant effects on indoor radon concentration. Ventilation rate is inversely proportional to indoor radon concentration. In general, all the results of indoor radon concentration are found to be well within the recommended action level (200– 300Bqm-3) by the International Commission of Radiation Protection (ICRP, 2009) but are on the higher side than the world average of 40 Bqm-3. Also the values of effective dose levels are found to be lower than the average value of 2.4 mSvy-1 given by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000).