A simple colorimetric fluorescent chemosensor 1-[5-(2-chloro-6-methylquinolin-3-yl)-3-(2-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethan-1-one (L) based on pyrazoline has been designed, synthesized and characterized. The sensing properties of L were studied using UV–visible and fluorescence spectrophotometric analyses. L showed excellent selectivity towards Zn2+ ions over other metal ions in aqueous