Abstrak Tujuan penelitian adalah untuk mengetahui pengaruh ukuran perusahaan, struktur modal, kualitas akrual, dan Investment Opportunity Set terhadap kualitas laba. Populasi dalam penelitian adalah seluruh perusahaan manufaktur yang terdaftar di Bursa Efek Indonesia tahun 2008-2009. Pengambilan sampel menggunakan teknik purposive sampling yaitu pemilihan sampel dengan kriteria tertentu, sehingga didapat sampel dalam penelitian ini sebanyak 31 perusahaan manufaktur. Hasil penelitian ini menunjukkan adanya pengaruh secara simultan antara ukuran perusahaan, struktur modal, kualitas akrual, Investment Opportunity Set (IOS) terhadap kualitas laba. Pengujian secara parsial menunjukkan bahwa variabel kualitas akrual dan Investment Opportunity Set (IOS) berpengaruh secara positif terhadap kualitas laba, sedangkan ukuran perusahaan dan struktur modal tidak berpengaruh terhadap kualitas laba. Abstract The research is to analyze Influence of Company Size, Capital Structure, Accrual Quality, and Investment Opportunity Set (IOS) on Earning Quality. Population in the study were all manufacturing companies listed on the Indonesia Stock Exchange in 2008-2009. Sampling was purposive sampling technique is the selection of samples with specific criteria, so that samples obtained in this study as many as 31 manufacturing companies. The results of research indicate the simultaneous influence of firm size, capital structure, accrual quality, Investment Opportunity Set (IOS) on earnings quality. Tests showed that the partial accrual quality variables positively affect the earnings quality, and the Investment Opportunity Set (IOS) is a positive effect on earnings quality, while the firm size and capital structure does not affect the earnings quality.