Although Japan has been a signatory to the Framework Convention on Tobacco Control since 2004, progress in translating the recommendations into national policy has been limited. Globally, outdoor smoking bans cover outdoor dining areas, beaches, public parks, schools, etc. In Japan, most of existing outdoor smoking bans allow designated smoking areas (DSAs) in the no-smoking zones, thus limiting protection from second-hand smoke (SHS). We examined the impact of DSAs on air quality in the areas of Kobe City where such ordinance is in force. Air quality measurements were conducted near two DSAs in August 2012 by using personal aerosol monitors. Three measurements were performed, each for 15 minutes, by four investigators: a line-up measurement, a vertical and horizontal measurement, and a circle measurement. In the line-up measurement, over 150 m/m3 of PM2.5 was detected by the monitor four metres from the ashtray, gradually reducing as the distance increased. In the vertical and horizontal measurement, 80-・10 m/m3 of PM2.5 was detected at 4, 11, 18 and 25 metres. In the circle measurement, similar concentrations of PM2.5 were detected at all testing points (mean concentration 94 m/m3). The study indicates that DSAs are sources of SHS in zones where a street smoking ban is in force, since SHS spreads widely, both vertically and horizontally. Street smoking bans that permit DSAs strongly limit protection from SHS and should be eliminated if protection against SHS is to be effective where such bans are in force.