We report on an optofluidic gain switch based on polydioctylfluorene solution in a femtosecond laser fabricated microchannel. The solution provides a stimulated emission cross section of the order of 10−16 cm2. Depending on the good isolation of polymeric chains we obtain ultrafast gain switching with time constants below 150 fs and high on/off ratios (up to 100%) in a broad spectral region (450–500 nm). This enables potential modulation rates well in the terahertz range. The enhanced optofluidic functionalities combined with the flexibility of femtosecond laser micromachining pave the way to an innovative class of optical devices easily integratable in complex systems.