A damage detection method using natural frequency and strain mode shape calculated from dynamic strain date obtained by distributed fiber optic sensor is presented. An analytical model for cracked beam is used to calculate the natural frequency and strain mode shape for damaged beam, and damage location and severity are estimated based on neural network technique using the measured natural frequency and strain mode shape. An experimental study was carried out on a cracked cantilever beam to verify the present method for damage identification. The cracks were inflicted on the beam and free vibration tests were performed for the dynamic strain data from the distributed fiber optic sensor. The damage estimation was carried out and it has been found that the identified damage locations and severities agree reasonably well with the inflicted damages on the structure.