MWCNTs/poly (pyrrolyl methine) composites with the different contents of MWCNTs were synthesized by in-situ ultrasonic polymerization, and their structures and photophysical properties were also investigated. The results revealed that the third-order nonlinear optical susceptibility of MWCNTs/PHPDTBE composite showed a rapid increase with the increase of MWCNTs' content, and obtained a maximum value of 3.41 x 10(-7) esu, which was almost ten times larger than that of PHPDTBE of 3.49 x 10(-8) esu. The enhanced optical nonlinearity was attributed to strong photoinduced electron transfer from PHPDTBE to MWCNTs by right of their strong noncovalent pi-pi interaction in the photoexcited state. (C) 2016 Elsevier B.V. All rights reserved.