Lasing of W3 and W2/3 triangular lattice photonic crystal waveguides on InP substrate is investigated around 1.5 μm by optical pumping. The lattice period of the fabricated structures is varied from 320 to 540 nm by steps of 20 nm, thereby leading to a detailed exploration of the lasing mechanism over a large frequency range. A distributed-feedback-laser- (DFB-) like-emission is observed above the gap (W3), while a genuine DFB laser emission is obtained in the gap (W2/3). Side-mode suppression ratios can reach 40 dB when an antireflecting coating is used on the cleaved output facet. Experimental results including light–light characteristics are analyzed in the framework of two-dimensional plane-wave calculations.