A cylinder lubricating oil composition for a crosshead diesel engine equipped with a scrubber, including: a base oil; and (A) a metallic detergent, wherein the composition has a base number of 15 to 125 mgKOH/g, and a kinematic viscosity at 100° C. of 10 to 30 mm.sup.2/s; and the composition satisfies the requirement (i) or (ii): (i) the composition includes: (B) 0.02 to 5.0 mass % of a demulsifier; (ii) the composition includes, as the component (A), (A1) a Ca phenate detergent; and (A2) a metallic detergent other than Ca phenate; the composition optionally includes (C-1′) 0.015 mass % or less in terms of nitrogen of a succinimide dispersant or a borated derivative thereof; and the Ph value of the formula (1) is 20×10.sup.−3 or less:

Ph value=C.sub.Ca×2/(r.sub.M×40.08)  (1)

wherein C.sub.Ca represents calcium content (mass %) derived from the component (A1), and r.sub.M represents a metal ratio of the component (A1).