In order to evaluate the effects of putrescine on marigold plant ) Calendula officinalis ( tolerance to some photosynthesis inhibitor herbicides, two pot experimentwere conducted under growth chamber condition in college of agriculture of Isfahan University of Technology, Isfahan (Iran), during 2014-2016. The first experiment was performed as factorial, based on the randomised complete block design with 27 treatments and 4 replications. Experimental treatments were 3 putrescine concentrations (0, 150 and 250 mg/lit), different types of herbicide (phenmedipham + desmedipham, bentazon and metribozin) and three concentrations of each herbicide (0.75X, X , 1. 25X, that X is equal to the labeled rates,1096, 1440 and 700 kg active ingredient ha- 1 ). The second experiment was conducted to examine the efficacy of phenmedipham + desmedipham herbicides along with putrescine pretreatments at different growth stages of marigold. 27 experimental treatments including 3 growth stage (4,6 8 leaf pair stage), 3 content of putrescine (0, 150 and 250 mg/lit) and three concentratio of phenmedipham + desmedipham herbicide (0.75X, X , 1. 25X, that X is equal to the labeled rates,1096 kg active ingredient ha- 1 ) was arranged in factorial, based on the randomised complete block design in 3 replications. The result from first experiment showed that phenmedipham + desmedipham caused minimal crop injuries i.e., destruction of leaf chlorophyll in labeled or lower application rates. The results oftheecond experiment revealedthat putrescence application have no effect on marigold phytotoxicity, cartenoid content, malondialdehyde (MDA) concentration, flower harvest index and flower numbers. Thought, pre treatment with putrescine (150 mg/lit) led to increases of SPAD value, ascorbat peroxidase activity, flower dry weight, leaf number and total dry weight of marigold. While, putrescine at 250 mg/lit led the increase in catalase and peroxidase activity. Phenmedipham + desmedipham herbicide application led to increased MDA concentration and hydrogen peroxide, catalase and ascorbat peroxidase activity, marigold phytotoxicity and led the decreases in peroxidase activity, flower harvest index, flower number (at labeled or higher rates), flower dry weight, leaf number and shoot dry weight. Results also showed that phenmedipham + desmedipham herbicide must be applied after the 6–leaf-pair stage of growth to avoid severe injury. Injury was lowest when applied at the marigold 8–leaf-pair stage. Protective effect of putrescine against herbicide stress was more pronounced at the later growth stage. So, marigold at 8 leaf pair stage was found to leave the greatest catalase and ascorbat peroxidase activity and decreased MDA concentration. At 8 leaf pair stage, phenmedipham+desmedipham (0.75 labled rates) along with putrescine application (150 and 250 mg/lit) and phenmedipham + desmedipham (labled rates) in combination with putrescine application (250 mg/lit) led to increases in flower harvest index, flower dry weight, leaf numbers and shoot dry weight. It seems that the latter treatments are good options because they protected yield with minimum levels of crop phytotoxicity; but we should consider that selective chemical weed control in marigold is limited because of it low tolerance to herbicide in earlier growth stage and growers must be applied other weed control strategy in early growth season to avoidance crop yield loss. Keywords :Calendula officinalis, Growth stage, phenmedipham + desmedipham, Putrescine,