This study was conducted to examine the relative tolerance of grafted watermelon to sub-optimal growing temperature conditions. Watermelon cv. Aswan scions were grafted onto different rootstocks, namely Giada, Shintoza, StrongToza, and Ferro. Grafted and un-grafted seedlings were grown in the field under low temperature during Jan.-Apr. to be compared to those growing under normal warm season conditions (Mar.-Jun.). Results indicated significant decrease in growth, yield, chlorophyll, and carotenoids in all grafted plants, in different degrees, depending on the graft combination. In this regards, plants of Aswan/Ferro recorded more than double the marketable yield of un-grafted ones under sub-optimal temperature, indicating the relative tolerance of Aswan/Ferro to cold stress. While, un-grafted plants exhibited the highest decline in all growth and yield parameters. Leaf proline content and the activities of anti-oxidant enzymes (SOD and CAT) were higher under cold stress than the control. It is concluded that grafted watermelon plants were relatively tolerant to sub-optimal temperature than un-grafted ones which could enable the production of out of season crop.