Poznański was also a philanthropist, and donated the first 10.5 hectares of land for the establishment of the New Jewish Cemetery in Łódź, which was the largest Jewish necropolis in Europe at the time. He and his wife Eleonora Hertz Poznańska were buried in a grand mausoleum on the cemetery, which has been described as "probably the largest Jewish grave monument in the world."
After his death, Poznański's complex of mills in Łódź were turned into the Manufaktura mixed-use development, which includes a mall, multiple museums, a hotel, restaurants and a multiplex cinema. The mausoleum and mosaic covering the inside of the dome were restored in 1993.