We study the differential equations w2＋ R（z）（w（k））2 = Q（z）, where R（z）, Q（z） are nonzero rationalfunctions. We prove （1） if the differential equation w2 ＋R（z）（w＇）2= Q（z）, where R（z）, Q（z） are nonzero rational functions, admits a transcendental meromorphic solution f, then Q= C （constant）, the multiplicities of the zeros of R（z） are no greater than 2 and f（z） = √C cos α（z）, where α（z） is a primitive of 1 such that √C cos α（z） is a transcendental meromorphic function. （2） if the differential equation w2 ＋ R（z）（w（k））2 = Q（z）, where k ≥ 2 is an integer and R, Q are nonzero rational functions, admits a transcendental meromorphic solution f, then k is an odd integer, Q ≡ C （constant）, It（z） ≡ A （constant） and f（z） = √C cos（az ＋ b）, where a2k = A1/A.
