A total of 60 adult guinea pigs of homogenous weight (250-350g) were used for evaluation of the appropriate quarantine period (1-5, 6-10 and 11-15 days post arrival) of laboratory guinea pigs before using the animal for experimental work. On arrival, the animals were allotted into 6 cages (10 animals of the same sex / cage). Feed intake, body weight and weight gain, growth rate, feeding behavior, and cortisol level were recorded for the animals during the different periods. Guinea pigs were also tested as experimental animal for evaluation of X-product toxicity, as indicated by two indicies (weight gain and mortality) during one week post injection, The highest stressful effect of transportation appears mainly during the first few days post arrival (1-5d), where guinea pigs recorded significantly the worst performance and behavior, and the highest cortisol level. However, during the second period (6-10d), the animals tended to modulate themselves and acclimate successfully to the surrounding environment through increased feed intake, attaining more weight, with lower morbidity and cortisol level. Meanwhile, by increasing the quarantine period to more than 10 days, the performance of the animal tended to redecrease again to values lower than that of the second period (6-10d) but still better than those of the first one (1-5d). Safety test results indicated that, the best performance was met in animals injected 10 days post arrival, while the lowest was obtained when the animals injected after 15 days post arrival, It can be concluded that, the stress of transportation and receipt of animals into new environment extended for at least 5 days post arrival, The period from 6-10 days is the best suitable period of acclimatization and stabilization of the animal behaviourally and physiologically. Increasing the quarantine period for more than 10 days is not preferable as the animal may be exposed to adverse management conditions that reduce its performance again. Therefore, a quarantine period not less than 5 days or more than 10 days with average 7 days post arrival is recommended for successful acclimatization of the laboratory guinea pig before its use in experimental purposes.