Constantin I. Istrati (7 September 1850 – 17 January 1919) was a Romanian chemist, physician, and politician.

After collaborating with Carol Davila, Istrati pursued his studies for three years at the University of Paris, where he obtained in 1885 a Ph.D. in Chemistry under the direction of Charles Adolphe Wurtz and Charles Friedel, with thesis On colored ethylbenzene and some observations about boiling points in the aromatic series.

[1] In 1883 he was named Professor of Physics at the School of Bridges and Roads in Bucharest, replacing Emanoil Bacaloglu.

He served as Minister of Public Works in the first government of Gheorghe Grigore Cantacuzino (April 11, 1899 to January 9, 1900), and as Minister of Agriculture, Industry, Trade, and Domains in the second Cantacuzino government (February 26 to March 12, 1907).

He is buried at Bellu Cemetery in Bucharest;[3] next to his tomb there is a bust of him, designed by the sculptor Raffaello Romanelli.