A survey of 185 weanling pigs, with ages ranging from 32 to 75 days, in 25 commercial swine farms with herd sizes of 64 to 1,500 sows in Batangas province was conducted to determine the prevalence and intensity of Isospora suis infection. Fecal samples were collected and examined for coccidia using the McMaster technique and modified flotation solution. Only oocyst-positive fecal samples were subjected to repeated sedimentation and decantation procedures and the final sediment incubated with 2-3 drops of 2% potassium dichromate solution for one week at room temperature for sporulation. Of the pigs examined, 10.3% were positive for I. suis oocysts. Fecal oocyst counts of infected weaners ranged from 4 to 510 oocyst per gram of feces (mean 22.9 OPG). Feces from oocyst-shedding pigs with diarrhea were usually pasty and yellowish brown in color. This is the first published report of I. suis infection in weanling pigs in the Philippines.