In this investigation live diatom species were grown in sea water polluted with Kerosine and Mazot. The results indicated that the diatoms which tolerated petroleum pollution were the bentho-planktonic taxa Melosira moniliformis (O.Mull.) Ag. and Grammatophora marina (Lyngb.) Kutz. in comparing with the planktonic species Chaetoceros curvisetus Cl., Coscinodiscus granii Gough. and Ditylum brightwellii (West) Grun.. This latter species was the highly susceptible one. The effect of the two petroleum products on the growth of the investigated diatoms varied greatly. Whereas, the number of cells of the tested diatoms decreased under the influence of Kerosine, certain doses of Mazot had stimulatory effect on the growth of some studied diatoms.