An high performance liquid chromatography with solidification-floating dispersive liquid-liquid microextraction(SFO-DLLME) based on saturated medium chain fatty acid was developed for the determination of four ultraviolet filters in environmental water samples.Octanoic acid,saturated medium chain fatty acid with a high melting point and a density less than water was used as the extractant,of which the existence form was changed by adjusting the pH of solution.An anionic extractant was dispersed in the solution for extraction at high pH,while a neutral extractant with high hydrophobicity emerged for separation from water at low pH.After optimization of the single factor condition and calculation of response surface method,the optimal conditions were as follows:the volume of extractant,ammonia and concentrated sulfuric acid were 100 μL,100 μL and 1.2 mL,respectively.The linearity range for the four ultraviolet filters were between 0.01 mg/L and 10.0 mg/L,with their detection limits of 0.18-0.76 μg/L and enrichment factors of 42-49.The recoveries for the samples at three spiked levels ranged from 73.8% to 103%,with the intra-day and inter-day relative standard deviations(RSD) of 1.9%-9.6%.The proposed method was simple,rapid and environmentally friendly,which further broadened the application ranges and provided a new idea for the development of dispersive liquid-liquid microextraction.