The present investigation was carried out in Garo Hills District of Meghalaya. The objective of the study was to find out the variation in the cost of milk production due to the variation in the size of dairy units. There were 142 annual varieties, 31 alternate variety, 24 crossbred and only 3 combine breed cattle samples out of 200 samples selected by stratified random sampling technique. The milk producing dairy units were classified into small (1-3), medium (4-6) and large (7 and above) herd size category using cumulative square root frequency method. The average milk yield per day in litres for NDLC- Annual type, NDLC- Alternate type and Combine Breed for both milking and milch cows was found to be highest in small herd size category with 1 to 3 animals. But for milking Crossbred it was highest in large herd size category with ≤ 7 animals. For milch Crossbred it was highest with 4-6 animals in medium herd size category. The net return was positive only for small herd size category with `1.71 in NDLC- Annual type and negative for all the herd size of NDLC-Alternate type cows.For Crossbred it was positive and highest for medium herd size category with `263.76 and for Combine breed it was also highest for small herd size category with net return of `82.32 per milch cow per day.