The photodissociation mechanism of long-chain alkyl iodides and cyclic alkyl iodides at 267 nm were studied using ion velocity imaging technique. Speed and angular distributions of corresponding photofragments were obtained by detecting ion images of I*(5p2P1/2) and I(5p2P3/2). Relative quantum yields ф(I) and ф(I*) were also obtained. Iodine fragments in this study were both produced via direct and rapid dissociation of C-I bond after absorbing one photon of 267 nm. Compared to long-chain alkyl iodides, cyclic alkyl iodides have obviously different characteristics of angular distributions which the value of anisotropy parameter β for I is bigger than that for I*. And as the alkyl group becomes heavier, ф(I*) tends to decrease.