In this study, oil as a source of biodiesel from Nannochloropsis oceanica was extracted using organic solvent. The oil extraction yield and efficiency from dry and wet microalgae were investigated. The initial fatty acids content of the N. oceanica was 317.8 mg/g cell showing a high oil content over 30%. The yield from dry microalgae was higher than that from wet microalgae due to the inhibition of water. The yield by chloroform-methanol was the highest and the yield by hexane was the lowest. However, the total fatty acids contents with the chloroform-methanol were 678.7 and 778.2 mg/g oil under dry and wet conditions, respectively. The high oil extraction yield by chloroform-methanol reflected the fact that the extracted oil contained a high level of impurity. The hexane-methanol extraction from dry N. oceanica showed high oil extraction efficiency, 82.6%. The chloroform-methanol extraction under wet condition also showed high efficiency, 88.0%. While the hexane-methanol extraction from dry microalgae is desirable under low drying cost, the chloroform-methanol extraction from wet microalgae is desirable under high drying cost.