A double-stranded nucleic acid complex that can have an excellent activity is provided. In one embodiment, the present invention relates to a double-stranded nucleic acid complex having a first nucleic acid strand and a second nucleic acid strand. The first nucleic acid strand is capable of hybridizing to at least part of a target gene or a transcription thereof, has an antisense effect on the target gene or transcription product thereof, and has at least two morpholino nucleic acids The second nucleic acid strand has a base sequence complementary to the first nucleic acid strand. The first nucleic acid strand is annealed to the second nucleic acid strand.