The population dynamics of stem-borer weevil, Ceutorhynchus spp. (Col.: Curculionidae) was studied in canola under field conditions in some parts of Iran during 2016-2018. Larvae cause damage by feeding inside petioles, crowns and/or stems of the crop. Meanwhile, the biology and distribution of the pest have not been previously investigated in the canola fields of Iran. In the present research, the pest adult samples were collected from three 1-hectare fields in Mazandaran, Golestan and Lorestan provinces by yellow water traps at weekly intervals during crop growing season. For collecting weevil-infested crops and determining infestation rate, 10 quadrates (0.5 x 0.5 m) were used per field. The adult weevils collected by the traps were identified and the pest biology as well as the infestation rates of the crop by the weevils were studied. The results showed that in late November, the adult weevils migrated to canola fields and after feeding and mating, the females deposited their eggs into main veins, petioles of the lower leaves or inside the collar area of young canola plants and the emerged larvae penetrated the host plant. The three larval instars of this pest fed inside host plant tissue during autumn and winter until the mid-spring season. In late April, third instar larvae left the host plant, dropped on the soil for pupation and new generation adults emerged in May. The maximum infestation rates of oilseed rape by the stem weevil in Mazandaran, Lorestan and Golestan provinces were 20.1 +/- 1.4, 14.8 +/- 0.99 and 10.2 +/- 0.79%, respectively. In this study, flight and oviposition activity of adults and feeding activity of the first instar larvae were mainly observed in late November, which suggests this time is a suitable time for control measures, if necessary. As an integral part of pest management strategy in oilseed rape fields, determining the time of adult migration activity, oviposition and larval development of the weevil is necessary.