A field experiment was conducted at Rice Research Station, Tonekabon, Iran, to determine the effect of N rate on seed yield, protein and oil content of two canola (Brassica napus L.) cultivars. Two canola cultivars (‘Hayola-308’ and ‘RGS- 003’) and five N rates (0, 50, 100, 150, and 200 kg ha ), organized into a randomized complete block design with a factorial treatment arrangement and three blocks, were applied to plot areas. Results showed that N rate effect was significant (P < 0.01) for seed yield, protein content and yield, and oil yield but not for oil content. On the other hand, cultivar had only significant (P < 0.01) effect on seed protein and oil content. Moreover, the interaction between N rate and cultivar was significant at P < 0.01 for seed, protein and oil yield, illustrating that cultivars showed different responses to N rates for these traits. In general, the quadratic equation provided a good description of the relationship between seed, protein and oil yield and nitrogen rate. For ‘Hayola-308’, seed, protein and oil yield increased significantly as N application rate increased from 0 to 150 kg ha-1, but thereafter remained constant. In contrast, for ‘RGS-003’, seed, protein and oil yield increased significantly as N application rate increased from 0 to 200 kg ha . Therefore, at the highest N application rate (200 kg ha ), ‘RGS-003’ produced greater seed, protein and oil yield than ‘Hayola-308’. Averaged across N application rate, the seed protein content of RGS-003 was significantly (P < 0.01) higher than that of ‘Hayola-308’, while the opposite result was observed for seed oil content. This study demonstrated the differential response of two canola cultivars to N rate in terms of seed, protein and oil yield. Za določanje vpliva različnega gnojenja z dušikom na pridelek semen in vsebnost beljakovin in olja v dveh sortah oljne ogrščice (Brassica napus L.) je bil izveden poljski poskus na Rice Research Station, Tonekabon, Iran. Dve sorti oljne ogrščice (‘Hayola-308’ in ‘RGS-003’) sta bili posejani v petih obravnavanjih z dušikom (0, 50, 100, 150, in 200 kg ha ) v naključnem bločnem poskusu s faktorsko obravnavo v treh blokih. Rezultati so pokazali, da je gnojenje z N statistično značilno (P < 0.01) vplivalo na pridelek semen, vsebnost beljakovin in pridelek olja, ne pa na vsebnost olja. Po drugi strani sta imeli sorti statistično značilen vpliv (P < 0.01) samo na vsebnost beljakovin in olja v semenu. Še več, interakcija med obravnavanji z N in sortami je bila statistično značilna (P < 0.01) za pridelek semen, beljakovin in olja, kar kaže na različen odziv sort v teh znakih na gnojenje z dušikom. V splošnem je kvadratna enačba dobro opisala razmerja med pridelkom semen, beljakovin in olja z gnojenjem z dušikom. Pri sorti ‘Hayola-308’ je pridelek semen, beljakovin in olja statistično značilno naraščal pri uporabi od 0 do 150 kg N ha , potem je ostal konstanten. Nasprotno, se je pri sorti ‘RGS- 003’ pridelek semen, beljakovin in olja značilno povečeval od 0 do 200 kg N ha . Sorta ‘RGS-003’ je pri obravnavanju z največjo količino dušika (200 kg N ha ) dala večji pridelek semen, beljakovin in olja kot sorta ‘Hayola-308’. Povprečno je bila pri vseh obravnavanjih z dušikom vsebnost beljakovin značilno večja pri sorti ’RGS-003’(P < 0.01) kot pri sorti ‘Hayola-308’, obratni so rezultati za vsebnost olja. Raziskava je pokazala različen odziv pridelka semen, beljakovin in olja dveh sort oljne ogrščice na gnojenje z dušikom.