A simple, rapid, eco-friendly and effective microextraction procedure for separation and preconcentration of nonsteroidal anti-inflammatory drugs (NSAIDs) from bovine milk samples based on in situ deep eutectic solvents formation between menthol and NSAIDs and its solidification was developed. The procedure involved alkaline hydrolysis of sample matrix, mixing aqueous sample phase with molten menthol to obtain deep eutectic solvents and analytes extraction followed by organic phase (extract) separation based on its solidification. The conditions of in situ deep eutectic solvents formation were optimized and used for the HPLC-MS/MS determination of diclofenac, flurbiprofen, ketoprofen and mefenamic acid in bovine milk samples. The developed approach allowed to exclude matrixes effects and increase enrichment factors of target analytes. The LODs, calculated from the blank tests based on 3σ, were 0.01, 0.01, 0.01 and 0.03 μg kg^{− 1}, for diclofenac, flurbiprofen, ketoprofen and mefenamic acid, respectively. The procedure was successfully applied to the analysis of real samples.