Rapid‐frequency‐scan (RAFS) dye lasers have been developed for determination of instantaneous line profiles of neutral atoms and molecules. Two types of rapid‐frequency scanners are examined and their scanning performances are compared. One scanner is an e´talon driven by a PZT piezoelectrical element, and the other is an electro‐optical (EO) filter with a KDP crystal. The PZT scanner takes 4–5 &mgr;s to scan over the free spectral range (FSR), and the EO scanner can make faster scanning. The maximum scanning range is limited by FSR, and the static bandwidth is approximately 1/100 of FSR in both cases. In fast scanning, however, the dynamic bandwidth increases. The error in the single shot measurement is evaluated, based on an experimental result of the line‐profile measurement of Fe atoms.