Purpose It is important to assess the level of control in asthmatic children who were well-controlled and thus discontinued controller medications. Office spirometry has been regarded to provide objective measures. We aimed to see time changes in lung function indices measured by the office spirometry and their relationship to clues for asthma exacerbation after discontinuation of controller medications. Methods As a pilot study, a total of 20 well-controlled children with persistent asthma were included. After discontinuing controller medications, each made follow-up visits at the 2nd, 6th, and 12th week. At each visit, spirometric values before and after bronchodilators were evaluated by the office-based spirometer. Time changes and their relationship to clues for asthma exacerbation were assessed. Results Among 20 children, 13 (65%) were successfully followed-up for 12 weeks with asthma kept stable. They presented similar spirometric values (forced expiratory volume in 1 second [FEV1], peak expiratory flow rate [PEFR], bronchodilator responses [BDRs] based on the FEV1 and PEFR) across all time-points. No differences in spirometric values were found between those who were stable and those who exhibited clues for asthma exacerbation. BDRs calculated from FEV1 values (BDRFEV1) correlated well with those calculated from PEFR values (BDRPEFR). Conclusion When controller medications were discontinued in children with well-controlled asthma, many of them were able to maintain the stable condition. Since the spirometric measures including BDR failed to differentiate clues for asthma exacerbation, the usefulness of office spirometry needs to be reevaluated by the larger population of children with controlled asthma after discontinuing medications.