Method for measuring the properties of a liquid comprising the steps of: - generating a laser light beam from a semiconductor laser source comprising a laser cavity; - directing said laser light beam towards a conduit transparent to said laser light beam through which a liquid flows, inside said transparent conduit the power of said laser light beam being modulated due to retro-reflection of said laser light beam towards said laser cavity by suspended particles moving inside said liquid according to an effect of self-mixing interferometry, - detecting, through a first photodiode arranged downstream of said transparent conduit, the power of said laser light beam modulated due to said retro-reflection; characterised in that it comprises the steps of: - detecting, through a second photodiode arranged upstream of said laser cavity, the power of said laser light beam modulated due to said retro-reflection; - correlating said modulated power detected by said first photodiode with said modulated power detected by said second photodiode in order to improve the signal-to-noise ratio; - processing said modulated power detected by said first and second photodiodes (9, 13) through a processing and control unit, in order to obtain one or more of the following properties of said liquid: • average flowing speed of said liquid in said conduit, • flow rate of said liquid in said conduit; • presence of said suspended particles in said liquid, • average size of said suspended particles in said liquid, • average number of said suspended particles in a volume of said liquid • type of said suspended particles in said liquid. - generating a laser light beam from a semiconductor laser source comprising a laser cavity; - directing said laser light beam towards a conduit transparent to said laser light beam through which a liquid flows, inside said transparent conduit the power of said laser light beam being modulated due to retro-reflection of said laser light beam towards said laser cavity by suspended particles moving inside said liquid according to an effect of self-mixing interferometry, - detecting, through a first photodiode arranged downstream of said transparent conduit, the power of said laser light beam modulated due to said retro-reflection; - detecting, through a second photodiode arranged upstream of said laser cavity, the power of said laser light beam modulated due to said retro-reflection; - correlating said modulated power detected by said first photodiode with said modulated power detected by said second photodiode in order to improve the signal-to-noise ratio; - processing said modulated power detected by said first and second photodiodes (9, 13) through a processing and control unit, in order to obtain one or more of the following properties of said liquid: • average flowing speed of said liquid in said conduit, • flow rate of said liquid in said conduit; • presence of said suspended particles in said liquid, • average size of said suspended particles in said liquid, • average number of said suspended particles in a volume of said liquid • type of said suspended particles in said liquid. • average flowing speed of said liquid in said conduit, • flow rate of said liquid in said conduit; • presence of said suspended particles in said liquid, • average size of said suspended particles in said liquid, • average number of said suspended particles in a volume of said liquid • type of said suspended particles in said liquid.